Rough Idle and TERRIBLE fuel mileage

The first thing to do would be to get the trouble codes pulled. Any Advance Auto or Auto Zone will do this for free. That will help you out a lot.
The things that I would be suspect of that might not show up on a code test are the fuel pressure and maybe a bad O2 sensor. O2 sensors usually will come up in a code read, but what you are describing is either that or an exhaust leak near an O2 sensor. The leak lets extra air onto the senor so it thinks the eninge is running lean and it dumps more gas in it. So look for exhaust leak, test the fuel pressure with tool which you can borrow from Advance or Auto Zone and pull the codes.

There are two codes p0100 and p0403. I can't remember which was which, but one called out the EGR valve, which I changed, and the other called out either the MAP sensor, MAF sensor, and vacuum leak. Nothing about and 02 Sensor. Although, I have had a code for an 02 sensor in the past. By the way, these two code were pulled after I changed the EGR valve. Thanks for the quick response! I think the IACv with fisx the idle problem, but not the gas guzzling problem....thoughts?

P0100 is Volume Air Flow, VAF and P0403 is Exhaust Gas Recirculation Return Solenoid Malfunction, EGR.

You might try to clean the MAF with some MAF cleaner, but be very gentle as they are senitive. Again look for a vacuum leak as that would cause poor performance and gas mileage and check the EGR pipes around the exhaust. There may be a leak in the system causing the same sort of issue as with the O2 sensor.
You may have braoke something loose when you did the EGR so re-check your work and look for any metal along the pipe that may have been rusted and it gave way when you replaced it or simply dis-connected.

Thanks for the help. I'll look for the exahust leak and see if I can find anything. I'm confident I didn't break anything while changing the EGR. It was fairly simple to change, although the location was a pain (between the engine and the firewall). A small vacuum line, 2 small coolant lines, two bolts and the gasket. Although I don't work on cars, I do work on airplanes, so my maintenance practices are the same.

If you work on airplanes you must be EXTREMELY thourough. I used to work for DOD when I lived in DC and I did some work with F/A-22 and F/A-35. Pilots love the F/A-22 and of course would rather have two motors. The 35 is an impressive jumper though.
Good luck and let me know how things go and we can go from there.
Sometimes when a car has quirks that are hard to diagnose, going to online enthusiast forums are a great source. My GF had a 2007? Spyder and if it weren't for pics on enthusiast forum I would have never gotten timing belt done. Forum members go to a lot of trouble to take pics and type up walk throughs with them and work arounds. I want to say it was a 3DSM forum or 3rd generation eclispe or something like that. Anyway it was the best help because it was a bunch of people who live for the car and have seen it all including the hard to diagnose quirks some cars have and you can post and they are happy to help you or direct you to an old post.
Just a thought as it is a good thing to know for any Eclipse stuff. I will try to find the forum if I get a chance.

Thanks! I like to think I'm very thourough. Thats why at times like these, when I am beyond my capacity of what I know, I get frustrated. I know the car is getting too much fuel, thus the 50% cut in mileage...my mind understands that, but its the figuring out 'why' part that I get stuck. Like you said, something is telling th car computer to feed it more gas....but what part is telling it to do that? I know that if the car runs a certain way, and then runs better when I disconnect the IACV, that tells me its bad. UGH!! I'm ready to change the MAP, MAF and the IACV at this point, but 2 out of the 3 have a hefty price tag on them. So I don't want to just start changing parts, without the confidence that one of the parts will fix the vehicle. Thanks again for your help. I won't be able to get 'under the hood' again till the weekend, so hopefully I will have sopme good news to report then. Btw...where you 'used' to work, you hit the nail on the head! 15's and raptors!

Yes the Raptors are awesome.
When you get back to me tommorrow I will get a IACV test instruction set for you. it is actually simple. You just disonnect it with the electrcis still connected, sometimes coolant lines too, have a buddy turn the key and see if the solenoid/plunger moves. If you have not cleaned out the portsfor the IACV, it may be a good time to clean that and the trhottle body. When you do so always spray cleaner from the outside into the intake manifold so you don't cram deposits further into the ports. You might also need to check or replace the TPS if we have not discussed that. I will get with you tommorrow and get a fresh look at it. After 50 or 60 questions I kind of get them all muddled together.
I will reply ASAP when you post.

I want you to have this link on a Vovlvo I went back and forth with forver until it got straight. It hink the MAF is more of a suspect the more I think about it. After you read this, I remembered it as I was logging out, you might agree or dis-agree. Let me knwo what you think.

https://www.2carpros.com/questions/2005-volvo-xc70-car-stalls-after-starting-runs-maf-unplugged

I have read about that IACV test, but haven't tried it yet, but its definitly on the list of things to do. I'm very curious about it. Thanks. Is there a similar test for the TPS? I don't have a multimeter at the house, so my testing abilities are limited. I think I'll start with what the car is throwing at me via codes. EGR solenoid (p0403), and the MAP/MAF sensor(p0100) and go from there. I do question the integrity of the MAF sensor. While the car is running, I can tap on the top of the sensor, and the RPMs will change. I read the thread concerning the Volvo. What kind of test did he do to figure out the root cause of the loose clamp on the intake?

There is a voltage test for the TPS. There are three terminals on the TPS. I forget which two you put the positive and negative on, but you will see that pretyty easy. If you get the polarity wrong most multimeters just read negative voltage. When the TPS is closed it sholud read .5 Volts and at WOT it should read 4.5-5.0 Volts. Not all are adjustable. If you get a replacement BLOX makes an adjustable one. If you ever need aftermarket stuff, go to horsepwoerfreaks.com. If you get the right person they will remember me as I still talk to them. Not for parts as I don't have my 1990 Integra that I put a 1998 GSR JDM Motor and trans in. I totalled it. Just some bolt ons and an adjustable fuel pressure regulator with an AEM Air/Fuel ratio EUGO meterr for tuning and it was so fast. I beat a new mustang by a few car lengths. Then I got beat by an S2000, not a surprise. I did not have the redline set properly though, I was shifting at 6500 RPM and I set it to 8500 where it should have been and it pulled so hard all the way. I had it going 120 in third gear with a few RPMs left. Pretty sick but it takes a lot of HP the faster you go to gain speed so I guess it would have done 140+ or so. I don't remember the accident as I hit my head a few times. It looked like it bounced between the bash and the steering wheel because the wheel was bent backwards and I had a bald spot on my head in the shape of the steering wheel, I am so glad it grew back. I really misss it and the guys at HPF are real enthusiasts and are like having a Tech support person and Sales person all in one. They will give you EBAY prices if you ask too. Anyway, be careful when you drive because all I could have done was to have been messing with the radio or lighting a cigarette and where I went of the road was a drop off so I could not avoid the telephone pole I hit. In a fast car sometimes you don't realize how fast you are going. 55 MPH is slow in a 140 MPH car and you would not believe how I got cut wide open by the seat belt buckle. Think about the force it would take to cut someone open all the way to there abdominal cavity with a belt buckle. I have a scar across my chest from the seat belt. I know I am going on about me but whenever I have a customer with a fast car I just feel kind of obligated to tell them how quick things can happen as it does not take much pedal to get going another 20 MPH unlike other cars.
So, The BLOX TPS is slotted for adjustment. I actually found TPS adjustemnt in our manual. I am attaching instructions and FIG4 which is the pinout for the connector. If I captuered the MIRAGE stuff, just ifnore it, you don't need FIGs 5 and 6.
I found EGR tests and have FIG for them. The only MAP info I could find is to check for vacuum leak between it and manifold.
So, I am attaching all said stuff and the files are labeled and are jpegs.

I am not sure if images took to post. So I am sending them again, there was some error message I have never seen before.
Let me know if you don't get them. There are 7 files.

There, you should have them all now.

Yeah...they are all there. Can't thank you enough for all the input/incite. Sorry to hear about the accident, but glad to hear all is well now. I bought my Eclipse brand new (Dec 99), so I've had it for a long time. It's like a member of the family, and I'm not ready to give up on it just yet.....especially with today's gas prices. I'd much rather drive the Eclipse to/from work than my other vehicles. I will start turning wrenches this weekend, and I will post Monday... hopefully with some good news. I'm looking to change the EGR solenoid, MAP, and MAF. One at a time of course to see if there is any change. The TPS does have the elongated hole mounts for adjusting, so I'll look into that as well.

Ok. I had some time this morning to work on my Eclipse. I tried the IACV chaeck, and it checked out. IACv moved as advertised. I picked up a MAF sensor and MAP sensor from a local Pick and Pull the other day, and was eager to see what would happen. Changed them both, turned the key, and the car came to life! No hesitation, idled fine, throttle response was good. Pulled the MAP back off, and re-installed the original.....no issues. Must of been a bad MAF sensor. Drove the car to work (approx 20 miles) without any issues. Idled fine at every stop, bu thte big one was my gas mileage....the needle barely moved!!! Everything seemed great.....until! Pulled into the gym parking lot, went for a 2 mile run, showered, got back to the car, turned the key, the car turned over, then immediately died! Turned the key again, started, and died. The car didn't even try to catch itself. Idle didin't bounce or anything, it didn't drop to 300RPM, and then race back up to 1000RPM. As soon as I pulled my foot of the accelerator, it died. The last time I turned the key, I kept the RPMs up, and slowly removed my foot from the accelrator, and the car idled real low (approx 500 RPMs) but didn't die. Drove into work, and at every stop the car idled low, but didn't die.....came close, but kept a very low idle. Even with the AC on, it didn't die. I did mess with the TPS about a week ago. Do you think I should adjust it back to the original position since it has the slotted mount holes? I didn't change that EGR solenoid yet, could that be the cause? Thoughts?!

Since the EGR code came up, it must have something wrong unless the codes weren't cleared properly. There is a function in the scanner to clear codes. If you adjusted the TPS, you should adjust it back or even better adjust it using the information I sent you. It could very well be affecting the idle. Odd though that it worked fine for a while. Let me know what happens when you adjust TPS. Since you got the info you should at least check it after you put it where you think it was before.

I'm sure there are "proper" procedures for clearing the codes. All I'mm doing is disco'ing the battery for a while. Before I starting farting around with the TPS I marked the mount bolt and the mount with a dab or paint, that way I would kno where the original position was. I'm going by Auto Zone tonight to have the codes scanned again, to see if anything cleared, or anything else shows up. I'll post tomorrow what happens after I re-position the TPS. I don't have a multimeter so I can't do the voltage check on the TPS.

ok...stopped by Auto Zone on the way home and got codes downloaded. Little bit of a surprise. The code for the EGR solenoid showed up again.....no surprise. The surprise was 505 Idle Air Control. I thought I might get by without having to change it.....but now not so sure.

You might try cleaning out the ports when you replace the IACV. Just make sure you spray cleaner from outside in towards the intake tract of the manifold. Otherwise you mgiht push deposits farther into the ports. Even though it moved it may not be reacting correctly. The EGR vavle is a bit baffling since you double checked it. aslong as you are sure the seal is good to the manifold, I don't know what could be going on with that. I lost my access to my service manual but I should have it again soon. There may be a procedure for clearing codes and that would set the story straight.

I changed the EGR, but I think the 403 code is pointing more toward the solenoid. I ordered one from Auto Zone and I pick it up today.

Okay, let me know how it turns out.

Got the IACV changed, and the car idles/runs fine now.....but I pulled the biggest bonehead of the year move today. While under hood today, I decided to change my thermostat. Not for any particular reason, other than the car has 175K miles with the original thermostat. Finished everything else up, and headed to work. After about 10 miles, whil eat a stop light I looked at my temp gauge and it was on the high side. I thought to myself....thats odd....maybe I got a bad thermostat from Auto Zone. The a little light bulb went off in my head. Take a guess what I forgot to do after changing the thermostat.

I spoke too soon. The same thing happened today, that happened yesterday. Car seemed to run fine, drove to work without any problem, went out to the car to go pick up the EGR solenoid I ordered, car started, then died. Had the codes pulled when I got to Auto Zone, and 403 and 505 again. Car idles kinda low, once it warms up and holds the idle. Idles at approx 500 RPMs. Frustration has set in!!!

If the IACV has coolant lines running through it, you might have some air in the system and it might be affecting it. If this is true, let car cool off, turn heat all the way up and take radiator cap off. Let the car reach opoerating temp and add coolant. Also look for foam in coolant as that is indication of air inssytem. Repeat process once if you note foaming or coolant level is not full or if idle is still low.
you might also need to clean the ports out that the IACV opens to control the idle. They start on the outside of the throttle body just in front of the butterfly valve and end just inside the intake manifold near entrance. Spray cleaner from outside in towards direction of air flow as doing the sopposite can make deposits go deeper into ports.
I am not sure what else could affect idle except TPS.

There are no coolant lines on the IAVC. No foam in the coolant. Coolant looked pretty clean. Had a nice florescent green color to it. No discoloration at all. I'm going to remove the entire throttle body so I can actually hold in my hand to examine, and I will do another check on the IAVC. I'm also going to change the EGR solenoid. I don't think it has any effect on the idle, but it needs replaced to fix the 403 code. I'm starting to wonder if there is a short going to the IAVC. If the IAVC check fails tomorrow, I'm gonna start looking at wiring. Unless the IAVC I picked up from salvage was on the fritz also. It came out of a 2002 Eclipse with the same 2.4l 4 cyl engine.

Yes even if it moved it does not mean it is moving as it should. I forget, did you ever get an IACV code?
You never know about the EGR. I don't know if it is possible for it to have a vacuum leak there or allow too much flow at the wrong time but it is worth trying at this point since you are getting down to the wire on options for the problem source. Daignosing can be really tough sometimes. All you can do is logically eliminate possibilities and you have certainly done that. The only thing I have not done is give you our link to a diagnostic walk through for engines with rough idle issues. There are several of them that are based on; "Performance loss", "Surging Idle", etc. So I will give you the rough idle just for the sake of having it to look through to see if there is something that has been overlooked as a possibility. If you want any of the others, just let me know.

Here is the link;

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Looking back through posts I thought you might want, "surging Idle"

https://www.2carpros.com/articles/engine-surges

I Also was thinking about the fact you ran a can of SEA FOAM which is good. But I reccomend if you have never run a fuel system cleaner to use two cans of BG44K. It is literraly a miracle worker and it removes so many deposits, which end up in the oil, that you have to change the poil after using it. Use One can per tank and then run a third tank without it before changing oil as it still takes some time for all depostits to work there way out. Sometimes the car may even run a little funny until the deposits are out and the computer adjusts. I used it on an olde motor that had a ton of crud on the pistons and was running on after it was turned off or dieseling. It cleaned the pistons off so you could see the tops of them. It made the oil black within three tanks of gas and it ran like crap at first and then it was better than ever. You have to go to a car dealership to find it and most dealerships carry it. You might call first. They also offer a direct injector clean but I think it is better to run through gas to get the whole system. It runs $20 per can or bottle but is worth it. You can also dump it in the vacuum hose of the brake booster to do a quick clean. But you end up smoking out your neighbors for five minutes or so and I don't think it works as well but techas have told me that it gets into other areas that adding to gas won't.
Anyway, just a thought. SEA FOAM is good but BG is truly better. It is caustic so be careful and have a rag and some water and soap if you think you might get it on your paint. I hold a rag under the bottle when I do it.

Yes I did get the IAVC code (505). I had the codes pulled again yesterday, and there were 4 codes 403 (x2) and 505 (x2). The weather has not cooperated today, so nothing was done today. Thanks a lot for the troubleshooting steps, I'll run them tomorrow.
So are you saying add one can to a full tank of gas 2 times, and on the third tank of gas DO NOT add the BG44K, and change the oil? One of the Auto Zone guys recommended Berryman B-12 Chemtool. He said the same thing about Sea Foam......"Sea Foam" is good, but the Berryman B-12 is better". He said the same thing about this stuff in regards to it removing paint, and to be careful. The Sea Foam that I ran was only added to the gas tank, nothing more, and it was only once. I've read about adding it to a vacuum line SLOWLY, let it sit for 20 mins, and then start the car, and smoke up the neighbors like you said. I've also read, some people have had some adverse reactions from it...especially to their 02 sensors. So I've been apprehensive about running it through via vacuum hose.

Yes, I don't really go with the method of dumping cleaner in the vacuum line or in any other way where it is not diluted with gasonline.
BG44K says that you at least need 10 gallons, or something like that, to treat fuel.
So, the method for using the two cans of BG44K is like you said;
Get a full tank of gas and add one bottle/can, they recently started putting it in bottles used to be in cans only.
Run that tank until near empty.
Fill the tank again and put in the second bottle of BG44K and at one or two points, drive the car a little high in RPMs. Stomping on it to where it kicks down a gear and changes RPMs quickly is good for high vacuum and the quick change helps to remove deposits. Don't rag on it just get on it once or twice. I got that advice a long time ago from a guy who builds some of the fastest drag motors in the country George Reggio. He said that any kind of performance motor does not do so well lugging it around all the time. They are meant to run, not be beaten or ragged on but run, and it helps keep them clean.
Run the second tank to near empty.
Fill the tank again without any cleaner.
When the tank is near empty or soon there after, change the oil as it will get dirty and even if it does not look dirty it is good to get the cleaner remains out of there just to make sure the oil is still up to its needed capabilities as additives can make it less capable of holding viscosity.
So, that is the full procedure with a little extra bit of advice I got from a pro. As I said the oil is compromised some with additives, so only get on it once or twice, some people think the car should be driven hard for the whole tank and that is not the best idea.
I have never heard of anyone who has usedB-12, but I have seen it but not to the extent that I come across BG44K in performance, Like Goerge Reggio swares by it, and almost every car dealership I have ever bought parts from has had it for sale at parts counter. I have paid up to $25 a bottle but $20 is a reasonable price.
Once you have cleaned it out good once, you can follow the reccomendations on the can which is every other tank. Of course they are trying to sell the stuff. I always run a can just before I change my oil or every other oil change and I have always found it keeps the combustion chambers really clean as well as valves and I have never had injector issues when using it.
So, it is something you should do anyway and it might just help the car performance issue as it can clean places you can't get to without tearing the motor apart.
Let me know the latest as I am keeping an eye on your replies.
If you want to get good aftermarket stuff for cheap, www.rockauto.com is unbeatable. They sell closeout stuff and you can literrally get $100 for $20 or even better from reman companys like Beck Arnley and Four Seasons. You have to for go the warranty, but it is so cheap and it is the real stuff. You can return stuff if it does not work or is the wrong part, but the long term warranty does not apply to parts they sell as they are closeouts. I got a windshield wiper motor from Beck Arnley for $15, $20 shipped. I have bought from them for years and always been happy with products. They have a great on line catalog too.

Ok...todays events. I removed the entire throttle body and cleaned it by hand. The only thing worth mentioning about that was this. On top of the throttle body are 2 vacuum lines one labeled "A" and on "E". I can only guess the "E" stands for "exhaust", because as I followed the line and it led to the bottom port on the EGR solenoid. The reason why I found this so interesting, is that this port on the throttle body seemed to be a little clogged. I blew into the port labeled "A", and found little to no resistance, but when I blew into the one labeled "E", it was difficult to pass air through. I don't know if this is normal or not, but after cleaning it, I was able to blow air through it a little easier, it wasn't freely moving through, but easier than before. As the throttle body was drying from the cleaner, I changed the EGR solenoid. I put everything back together, and did another check on the IACV, which seemed to move freely as before. With everything back together, I turned the key, and had to pump the gas peddle a little to keep it running, which I wasn't too concerned with because of the cleaning fluid. After I few pumps, the car idled fine. While I had the car idling, I used that Berryman B-12, into the vacuum line. I had to jockey the throttle to keep the car running, but I used about 1/3 to 1/2 a can and let it sit for about 30 mins. After that, I started the car, and little to zero smoke came out the exhaust, but I attribute that to the EGR valve I changed. Took the car for a test drive, and ran it pretty hard. Red lined once or twice and the car ran fine. Throttle response was ok, and idle was ok. The real good news is, for the first time in about 7 years, my check engine light is out, and remains out!! Thats a victory in itself! So for now, everything seems GTG! I'm going out to the car in a few hours to see if it act like it did Thursday and Friday. More to come....

That is great news. Isn't that the best feeling!
I am very glad to hear it is running well. Sounds like you got it. Sometimes the smallest things can cause so much trouble.
Really glad you finally got it.
Let me know if anything else comes up from it.
Otherwise, CONGRATULATIONS!

Thanks....I really appreciate all your help and attention. There are a few other small issues I'm having but this big one couldn't of been handled without your help.

Your very welcome. Thanks for your kind words. Not everyone thanks me and it is really cool when they do as I like doing this to help people. It is a really cool things the owners have going and the team of Techs are just great and they are from all over the world.
Come back any time you need help or advice.
Take care.

Dr. C

Well my friend...the joy of not having my CEL not coming on was short lived. It came on after about 15 minutes into my drive to work today. I pulled into Auto Zone, and codes P0421 (Warm up catalist efficency below thresh hold (bank 1) and P0505 (Idle Air Control). The car seems to be running fine. I'm beginning to wonder if I have a short somewhere in the wiring to my IACV, but that is above my trouble shooting capabilities. If I did have a short, wold it more likely be in the connector itself? If thats the case, I can splice a another on no problem. The 421 code....is that my )2 sensor aft of my Catylitic Converter?

It could be a hort, but it works and doesn't blow a fuse. Still could be a bad ground though. The IACV might be bad or you might need to clean out the throttle body better and maybe the intake manifold. Check that port to see if it clogged back up.
As far as the cat, I would think that the O2 sensor is the only way to detect the catylitic converters performance.
I hope it goes well as I can't run this thread any longer than I have. I have to get to other threads as the long line of customers grows if I don't have a limit to thread length. Most Techs only go back and forth once or twice, but I try to solve every issue I can. But, I always have a load of people that I have to get too and it all depends on how many people are in line for respones.
You can always re-post with new issue, or the same one and it might even be good for someone else to pick it up with new view.
I think I did ask a tech to look at it and he didn't have time because we have really grown and don't have enoguh techs for the workload. It comes and goes like that.
I wish I could help you more but I am actually out of ideas at this point anyway.
Good luck with everything and I don't think the diagnosis is out of your capability. You have the aptitude you just have never done it before and that is always something that holds me back. Just go with your instinct as you have and I bet you will get it figured out if you haven't already.
Take Care.
Dr. C

Hey bud did you ever figure out what was wrong I am having the same problem burning through gas like it is nothing.. it is very frustrating and also I'm burning oil

I have looked through our correspondence and their is so much that I do not see if you did a compression test or not.
I think with oil getting past the rings the O2 sensors are bad or failing and that will affect gas mileage a lot when they go bad.
Do a compression test to see how bad your ring seal is. If it is really bad you probably need to look into a used motor or a rebuild.
The best bet for a used motor is to get a JDM, you are fortunate you have a car that the engine will be available, engine. In Japan their is a law that requires a new engine or a new car at 30,000 miles. So, you can get used Japanses spec motors online easily. You can poften get them with a whole drivetrain for less than $3000. You can even change to a turbo motor as they will give you a wiring harness and ECU. You would then go to a place like, www.swapshop.com or www.rywiores.com to get your harnes fdor your engine converted and you will have a motor that is essentially new and they run better than the American spec engines.
Don't go to Panther motorpsorts in Canada. They are the only place with a bad rep that I have found. You can try to get Hmotororsonline.com to special order you one as they only do Hondas, but they are the best place. I got a GSR motor and drivetraing to my door for $3500 with LSD tranny and all wiring and ECU. It was like brand new. The owners name is Steve and might order you one when he has buyers in Japan get a batch. No one else has the reputation he has. But, if you research you can find other JDM places that have Mistu stuff. Try going to a mistu enthusiats forum, I believe there is one called 3gen.com or something like that.
If you have compression the valve seals are bad and that will get to your O2 sensros too and cause bad MPG.
So, Do the test, get new O2 sensors in either case for after the repair. If the valve seals are bad I would consider a JDM anyway as the head repair will cost half as much as a motor. If you do a straight swap you won't have to convert harness.
Don't install new sonsors until you install or fix the cars engine.
That is my best guess at this unless I missed something. We have gone back and forth a lot . But, that is about all that is left.