Idle air control valve?

You may have a vacuum leak, get a can of spray Throttle body cleaner, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! Idle control diagnostics: IDLE AIR CONTROL SYSTEM DIAGNOSIS 1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step. 2. Set parking brake and block wheels. Turn A/C off. Start engine and let idle. Install scan tool and select SPECIAL FUNCTIONS. Select IAC SYSTEM TEST, and then RPM CONTROL. Using scan tool, command engine speed to 500 RPM. If actual engine RPM is within 100 RPM of scan tool display, go to next step. If actual engine RPM is not within 100 RPM of scan tool display, go to step 4. 3. Using scan tool, command engine speed to 1200 RPM. If actual engine RPM is within 100 RPM of scan tool display, check for a non-IAC system problem (i.e., vacuum leak, sticking throttle cable, fuel system lean or rich, throttle body, poor electrical connections, faulty PCV valve, A/C compressor circuits). If actual engine RPM is not within 100 RPM of scan tool display, go to step 5. 4. Check for vacuum leaks, sticking throttle plates, faulty PCV valve, or restriction in air induction system. If problem exists, go to step 20. If problem does not exist, go to step 6. 5. Check for obstruction or excessive carbon deposit in throttle body IAC passages. If problem exists, go to step 21. If problem does not exist, go to next step. 6. Turn ignition off. Disconnect IAC valve harness connector. Check for poor connection at IAC valve. If problem exists, go to step 19. If problem does not exist, go to next step. 7. Connect IAC Driver (J-37027-A) to IAC valve. Set parking brake and block wheels. Turn A/C off. Start engine and let idle. Install scan tool and monitor engine RPM. Using IAC driver, extend and retract IAC valve. If engine RPM decreases and increases as IAC valve is cycled, go to next step. If engine RPM does not decrease and increase as IAC valve is cycled, go to step 22. 8. If RPM changes smoothly with each flash of IAC valve cycle, go to next step. If RPM does not change smoothly with each flash of IAC valve cycle, go to step 22. 9. Install appropriate IAC node light onto IAC valve harness connector. Cycle IAC driver and observe lights. Both lights should cycle Green to Red, but never off as RPM changed over its range. If lights flash as specified, go to next step. If lights do not flash as specified, go to step 12. 10. Remove IAC driver from IAC valve. Using DVOM, measure resistance between IAC valve terminals "A" and "B". See Fig. 8 . Also, measure resistance between IAC valve terminals "C" and "D". If resistance is 40-80 ohms on both measurements, go to next step. If resistance is not 40-80 ohms on both measurements, go to step 22. 11. Using DVOM, measure resistance between IAC valve terminals "B" and "C". See Fig. 8 . Also, measure resistance between IAC valve terminals "A" and "D". If resistance is infinite on both measurements, check for a non-IAC system problem (i.e., vacuum leak, sticking throttle cable, fuel system lean or rich, throttle body, poor electrical connections, faulty PCV valve, A/C compressor circuits). If resistance is not infinite on both measurements, go to step 22. 12. Turn ignition off. Disconnect PCM harness connectors. Check for poor connections at PCM. If problem exists, go to step 19. If problem does not exist, go to next step. 13. Remove IAC node light. Check for an open in IAC driver circuits between IAC valve harness connector and PCM harness connector. If problem exists, go to step 19. If problem does not exist, go to next step. 14. Using a test light connected to battery voltage, probe IAC valve harness connector terminals. If test light illuminates at any terminal, go to step 17. If test light does not illuminate at any terminal, go to next step. 15. Turn ignition on with engine off. Using a test light connected to ground, probe IAC valve harness connector terminals. If test light illuminates at any terminal, go to step 18. If test light does not illuminate at any terminal, go to next step. 16. Check for a short between IAC valve circuits. If problem exists, go to step 19. If problem does not exist, go to step 23. 17. Repair short to ground in IAC circuit. After repairs, go to step 24. 18. Repair short to voltage in IAC circuit. After repairs, go to step 24. 19. Repair circuit as necessary. After repairs, go to step 24. 20. Repair condition as necessary. After repairs, go to step 24. 21. Clean IAC passages. After repairs, go to step 24. 22. Replace IAC valve. After repairs, go to step 24. 23. Replace PCM. Program PCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step. 24. Install scan tool. Start engine and let idle. Turn off all accessories. Using scan tool, command engine speed to 1200 RPM, and then down to 500 RPM. Again, using scan tool, command engine speed as specified. If actual RPM is close to commanded RPM, system is okay. If actual RPM is not close to commanded RPM, go to step 2. 4/15/2010 ...

Thanks.


I tried the 'spray carb cleaner' (it's what I have on the shelf) to identify vacuum leaks. No changes in engine speed.
Also, to clarify last post. Reason we didn't have mechanic in small shop replace part is it happened on Friday nite & he couldn't get part till Monday. He said it could wait till we got back just be careful. Reason I said this is: He said he made adjustment to help compensate, till we get back home & that any mechanic will readjust it after replacing the air control valve. I don't know what adjustment he made. Please take a stab at it & tell me what it might be.

You rely on the 'Scan tool' for the technical repair. I do not have one. But could really use one since the 'extended family' has: 2000 Astro AWD, 2991 silverado truck, 1997 buick lesabre, 2003 GMC sonoma pickup ALL GM.
What would you suggest I buy, so I can do more of my own repair?


Thanks

What I need to know is does yours have the accelerator cable? Or electronic gas pedal? If it's cable operated, remove the cable from the throttle body, and see if it idles normally. if it does, the cable might have a burr inside the guide...replace cable. Does the plate close fully at idle? If not, it may need a new throttle body. And check for any PCV restriction.

Accelerator cable is OK. There is no tension on cable when pedal in 'unpushed' position. It operates smoothly still. However, when I push on the throttle body 'control' (where the accelerator cable attaches) to push it more closed, the idle Does Indeed slow down to what it used to do. Sooo, I just sprayed the heck out of the accel cable , return spring , & shaft shere goes into throttle body. A little more help. But spring does not close throttle plate all way since I can push it a bit more . What does that mean? Also, can you provide an answer to question on 'scan tool'?

Thanks VERY Much

About the scan tool, most generic scan tools cant do these particular tests, this is for GM Tech II scan tool. Check for wear inside the throttle plate area, and for in and out movement of the plate, it may need a new throttelbody, or possibly a new TPS...could be sticking?

It's Fixed!!
So, there is this Other cable that also attaches to same apparatus that accelerator cable attaches to. This Other cable goes up & around to the firewall & attaches to some black electronic component. It was This cable doing the 'final' sticking (preventing the throttlebody from closing) cause it was 'oriented wrong' & sticking. I used WD40 & got it freed up & now Everything works great!. Throttle body closed completely to what its supposed to & engine idle is down to Normal. Thanks for your help.
Oh, What is this other cable & what's it for? Any ideas?
Thanks again.

Cruise control would be my guess?

I am having a problem with my engine Idleing at a little fast when coming to a stop and after i stop seeming to want to keep moving.The Idle slowly comes back down as I am stopped but when I began to move and release the brakes I sometimes don't have to excerate much before it goes under its on power.It feels like the excerater is sticking or it is Idleing to high.Could this be a sticking IAC valve?

Try cleaning out the IACV and see what happens

check for a bind in the cables to and from the cruise control unit.

mickey-d

When I put parking in my van after driving the Service Engine Soon light comes one. After putting the van in drive it disappears. It was scanned and it shows IAC Valve problems. I replaced it, the code was erased and all that is supposed to be done. The thing is that I got the light on again in parking after driving it a while. I scanned it again, and it shows me IAC valve problems again. There is also a strange smell like paint or nail polish. Any idea what is causing this problem?

The common mistake is the diagnostic fault code did not say to replace the idle air control valve or that is was defective. Fault codes never say to replace parts. They only indicate the circuit or system that needs further diagnosis or the unacceptable operating condition. This valve has a very low failure rate, at least as far as electrical failures are concerned. You didn't list the mileage so I can't make any judgements related to that, but based on age, I'd start by checking the wiring for insulation that's rubbed through and a wire is grounding out, or possibly a corroded or stretched terminal in a connector. Your mechanic can also use a scanner to run the valve through its range of travel to evaluate its operation.

The mileage is 165,000. I was told to check the evaporative system too (I think that's the way it is called), which was done today to see if there is any leak, but the mechanic could not find anything. I would like to know if there is a kind of diagnosis that can be done to find where the problem is. Thank you for your response.

First you have to know the exact fault code number. There are about a dozen related to the idle air control valve, and they mean very different things. That system doesn't have anything to do with the evaporative emissions system. Also, that system, which is also referred to as the "vapor recovery" system, isn't monitored on '95 and older models, so while it could have a leak, that won't be detected by the Engine Computer and it won't set a fault code.

To find a leak in the vapor recovery system, you really need a smoke machine. That allows you to inject a white, non-toxic smoke at 2 pounds of pressure, then you can watch for where it sneaks out. Other than that you're limited to a visual inspection, and that is only good for real obvious problems. Most leaks in this system are way too small to see by eye.

For the idle air control valve circuit, I already mentioned checking for bare wires and corroded connector terminals. Beyond that the testing gets a little more involved. You can use an ohm meter to test the resistance of the wires and the motor that runs the idle air control valve, and I mentioned the scanner for running the motor through its paces to see if it responds properly. There really isn't anything you can do yourself when a scanner is required.

The code that is shown in the scanner is 35.

35 - Idle air control sensor circuit fault

As you can see, fault codes don't get real specific. To add to the confusion, the idle air control valve, (automatic idle speed motor), is not a sensor as the code implies. AND, . . . it's not a motor as we normally think of one that spins. This unit has four wires and four internal electromagnetic coils. It doesn't have brushes like most motors do. The Engine Computer pulses the coils with varying voltages and polarity to set the armature to the desired position, and as it rotates slowly, it extends a valve that is on the end of a threaded shaft. As that armature turns, it extends or retracts the shaft and valve to vary how much of a controlled air leak is exposed. As it opens the passage to allow more air in, the computer lengthens the amount of time it holds the injectors open to allow more fuel in. That is how the computer adjusts idle speed and holds it steady.

Remember too that this valve only affects idle speed, and nothing else. If idle speed is too low, you just have to hold the accelerator pedal down 1/4". The engine may be hard to start if you don't do that, and it may tend to stall at stop signs.

hi i have a 95 astro van that is really making me mad it idles rough even while driving.i have put my scanner on it also auto zones scanner on an both say no codes,i have replaced plugs wires cap and rotor,cleaned the iac ,checked vacuum lines,and checked fuel pressure,and still runs rough, now im tinking ing module?crank sensor or the computer all together????????? any help would be great next step is i stick of TNT and a match lol

Hello, Ok, with that year most fuel related problems won't set a code. I have come across this to many times and the people have checked and double check and still crossed wires. If firing order is correct then next step would be to check or just replace the Injector Assembly. I say replace cause it is located under the intake.

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is there any way you can send me that exploded view or the link to it? i desperately need it.

Here is the exploded veiw.....

Sir i owe you a case of whatever your favorit beer is that pic will undoubtedly save me alot of frustration and trouble.

Thank you ever so much for sending it too me.

Keith.

No Problem, let me know if you need anything else.

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well i got the new injection in but i have thus ran into two problems..one i think being huge.
1: i have no information telling me where each injector plug/poppet valve goes where no numbers or letters nothing...i dont want to blindly start plugging them into the wrong port. i was wondering if anyone has a detailed diagram/layout showing where each injector plugs into its proper port
2 on the electrical connector that attaches to the top of this assembly i found some black sticky goop that almost completely coats the entire connector...is this some means of protection/insulation for the connector? and if so can anyone tell me what it is and where to find it and if it is critical to the correct re installation of the new injection system?
any and all answers or help is greatly greatly appreciated.
thanks

Keith
working on a 1995 Chevy Astro with bad injection problems

Hey Keith,

It is simple once the assembly is installed there should be 3 lines on each side. And they go as they are, the one one either side toward front of engine go in socket at front of engine the ones in middle go to middle socket and of course the ones toward rear go the the rear sockets.

And I believe the tar like coating is a factory thing and doesn't have to be placed on new assembly.


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i got everything back in and its looking good,with no leaks or odd explosions of any sort lol.but now im at the stage where i need to bolt the upper intake plenum back on and i need the torque specs and bolt tightening sequence badly


again any information would be greatly appreciated and all the info from everyone thus far is thanked for a million times over.


Keith

Hey Keith, Guess I should have posted the specs also before you had to ask for them. Anyway, here they are.... Lower Intake Torq is 35 foot pounds

Upper Intake Torq Is 10 foot pounds

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ok now something is rotten in denmark,

i did everything like i should of and was told,installed the new injection system exactly like the old one,torque everything down properly,replugged all the sensors,reconnected the throttle linkage,put on a new coil and rotor,installed a new EGR but when i went too crank it today after checking and double checking and triple and 4th time checking, IT WILL NOT START.
i dont have a fuel pressure gauge so i dont know if im getting the proper fuel pressure to the new injection (heard it was between 45 and 65psi) would any new problem show up on a scanner? its not even acting like it wants to start,no thumping of the cylinders or anything.just sits and spins when i hit the key.

i simple cannot figure out why it wont start
any ideas guys?

any and all help is greatly appreciated

thanks

Keith.

ok i forgot a few things from my last post a few min ago

i cleaned the upper intake port with some MEK because one of the holes (the on closest to the EGR thats about the best i can explain it.)
was almost completely blocked by carbon build up,
i poured just a tiny tiny amount of MEK(read it was the same thing in gumout carb cleaner) ,about a table spoon into it..after some set time all these big ping ball sized chunks and nuggets of carbon came falling out after i let it set for about 10 to 15 to work and a 2 days to dry out,the MEK cleaned the gunked up hole like crazy but im wondering if it might of damaged one of the sensors resulting in it not being allowed to start
also there was some black tar like goop on the electrical connector for the new injection since most of the gunk left with the old injection i used black ATV sealant..i connected the connector made sure it was good and locked down, then shot a bead around it figuring it would protect it from any kind of leak. could this of been a mistake as well?

ive went over every single connection, and i just cant figure out why it wont start,

if anyone has an idea please please let me know.


Keith.

Ok, did you check to make sure you have good spark? I know you said you replaced the coil, but, you could have gotten a bad coil.

Do you hear the fuel pump turn on when key turned to on position? If not relays and check fuses.

If you have a local rental store see if they have a fuel pressure tester.

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no i didnt replace the coil,just the cap and rotor,i held the "coil" wire against a bolt stud and hit the key and got a good solid arc . its just not firing for some reason.
it will do a funny kinda hesitate afer it runs through a few cycles...kinda like it "seizes" but wont fire off...sorry but its very hard to describe.

im thinking perhaps i got my plug wires mixed/ on wrong or i don't have enough pressure to the injection system(they said the poppet valves wont open till 45 psi)..but if anyone has any more ideas please let me know...this is only the 3rd car i have ever worked on..im used to a 89 ford Thunderbird and a 85 camaro berlinetta and that is the extent of my automotive knowledge.


thanks for the info guys.

Keith.

Ok, what color was the spark? It should be a Bright Bluish/White. If Orange spark is weak and possibly need to replace coil.

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yep real strong bluish white spark.

well i got it too start, was a simple mix up of the plug wires, but i still have two problems

1: im still getting fuel alll down in the oil pan,when i do the screwdriver trick and use a stethoscope i can hear it trickleing

2 its stuttering for some reason,im thinkinging this is caused by bad plugs,going to change them tomorrow

does anyone have any ideas why the fuel would be getting down into the oil? cause im at a loss on this one..

thanks for all your input and please keep it coming


thanks

Keith.

Where and when are you listening with the Stethoscope? If listening at the block with engine running or just after turning engine off then most likely what you are hearing is the oil returning to the oil pan and not fuel. And if you haven't changed the fuel filled oil then it will sound pretty much like water running.


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i used the steth all over the engine ,upper intake is where i hear the trickling sound the most and the clearest,and it does sound like running water,but i have changed the oil 3 times so far in the last few weeks,(dont want any explosions) also my white smoke problem persists,was told it might be steam from coolant getting into the combustion chamber,but the thing is its been cold the past few days,steam is hot and i would think it would rapidly vanish in cold air,this white smoke does not vanish but lingers on for quite some time,im thinking that its not steam but something else,but cant figure out what would cause white smoke,gasket burning,junk burning? perhaps somethin in the catalytic converter burning?

any ideas would be appreciated.

thanks

keith.

Has the Oil smelled like gas each time you change it?

The White Smoke can be either that you have a blown head gasket or intake gasket.

Also if I am not mistaken that year has a Modulator Valve on the passenger side of the Tranny and it uses Vacuum. So, if it is going bad then Tranny Fluid is being sucked into the engine and being burnt in the cylinders causing the white smoke.


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yeah its smelled like gas bad all the times i have changed it...it was really bad with the old injection system,with this new injection system its not as bad but still there enough to cause problems.....i simply cant figure out how the fuel is getting into the oil with a new injection system installed....

i didnt know that the tranny could be the cause of the white smoke,are there any other symptoms that could help diagnose if the modulator valve is indeed bad? like bad shifting,hurky jerky shifting at speed? no shifting at all etc etc,,,,i haven't gotten it out on the highway yet to see what other problems are lurking in here.just been driving it down to the store for groceries since the new injection was in. but at 20 and under it seems to be shifting fine. but who knows what its going to do at 70.

thanks guys

Keith.

You may not notice any shifting problem till the fluid level gets low, since it isn't an internal problem and the modulator would be working it would just also be sucking tranny fluid into engine.

You can check the Vacuum line coming out of the Modulator and if it has fluid in it then it is bad.

Have you had a chance to check Fuel Pressure. If not you can pull each plug and check for Fuel on the plug. If any or all smell like fuel then you may have a fuel pressure problem.


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i havnt gotten around to changing the plugs yet,but will keep that in mind,and since im on a fiber optically thin budget it might be a while before i get the fuel pressure tester,dont even have the cash to rent it right now.life suck without a car and it sucks more when you dont have a job.

as a side note how to if find out what kind of tranny i have?..i was told that if its a 4L60E there would be no modulator,but i havt no clue what i have and dont feel like dropping it to check out some numbers....is there a quicky route i can take?

thanks guys

Keith.

Post your vehicle info...

Year

Make

Model

Sub-Model

Engine Size in Liters

Vin#

and crawl under and count the bolts on the tranny pan. Or if you can take a pic and post. And I will check it out for you.


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