rough idle in gear 1990 mirage throttle position sensor or idle speed

i would look for a vacuum leak. have the intake system smoke tested to find it. intake gaskets are common.

Roy

Some trouble codes do not trigger the CEL for older models so it is good to check for trouble codes.

https://www.2carpros.com/articles/mitsubishi-trouble-code-definitions-and-retrieval-procedure-for-odb1-system

Try above link if you want to check for trouble codes.

If I have no CEL do I have codes?
Do notice what sounds like an exhaust leak that I only hear in gear stopped at traffic and after isc lowers rpms revs back up then drops to rough idle.

Thanks this is driving me nuts. 1 month and no one has a solution. Will get smoked and advise.

I am correcting original post. Transmission jumps in / out of gear most notably when I'm off the gas. Also seems to shift prematurely. Thanks again.

Not all codes trigger the CEL and for transmission, most codes do not show unless you use the diagnostic method to check.

If you are not going to follow advise, I will stop here.

Have a nice day.

Smoke test was negative. Maybe I led on to know more than I do. How do I perform code check via diagnostic method? Thanks!

For engine trouble code, click the link provided in previous post.

Transmission Self-Diagnostic Test Procedure

Connect analog voltmeter or LED lamp to diagnostic connector terminal No. 10. and ground. See Fig. 7. Turn the ignition switch to the ON position, and TCU memory contents will start immediately.

The sweeping needle of the analog voltmeter or the blinking LED lamp would indicate the fault code.

Mechanic says he doesn't have software to run an engine diagnostic code check? Is there special software required? He did find fixed idle and set idle screws "way out of specs". No more revving / wandering RPMs but still rough idle in gear at full stop. I hear a slight exhaust (?) leak only when: lights on, turn steering wheel, press brake pedal when in gear does seem to coincide with rougher idle. Mechanic says its negligible and thinks its as good as its gonna get. I can't believe it. He says 10 cycles of 35 mph to 55 mph required to recalibrate ECU/ECM. And to run a tank of Hi Octane to smooth it out.

The car wants to run smooth in gear and does momentarily on slowing down but once at a full stop starts running rough & shaking. It smooths out as soon as I let off brake and start to roll just a little. Will try a trans specialist (AAMCO?) for Trans codes. Thanks again.

Did you read my replies? I outlined the procedures for retrieving both engine and transmission trouble codes.

Your idling speed is too low and not stable. If you did not clean the throttle body, do so. Have the valve clearances checked as well.

No codes on engine or trans. cleaned throttle body no difference. latest mechanic says torque converter is bad. going for rebuilt trans - any suggestions or good prices - or places to steer clear of? I see rebuilds for $500 sound about right to you? Thanks again.

New trans and valve adjustment did not solve my problem. Idle is only rough now when engine warms up. Mechanic retarded (?) timing and lowered idle. I am noticing ping and knock i did not have before.

Check the throttle position sensor adjustment. Have a cpompression test done.

Compression test passed. Throttle position sensor adjusted. Idle/timing set to factory specs by Mitsu. Still rough idle. Now throwing CEL code for O2 sensor. Replacing today. Car still has rough idle in gear when warm and is exacerbated with any load (electrical) on engine (lights, brake, a/c). Also notice no high/warm up rpms. Rpms never change despite engine load or temp. Also with a/c and warm engine will idle so low and rough feels like pending stall. Thanks.

Does/how the new ecu sync with new ISC? Is it necessary?

ECU would self learn after some driving time. What were the compression test results? Any vast differences among the cylinders?

If the cold start system is not working, I believe the ISC is stuck. You might need to recheck the ISC and if necessary replace it. The other thing would be the MAP sensor. It often fails and causes the symptoms described.

Dont have specifics on compression test but nothing significant was found out.

The ICS is new from Advance Auto - but I think you're right - how can i check it? MAP sensor? Please let me know how to locate and test if possible. I am noticing low idle rpms when the engine is cold and higher rpms when it is hot? Any ideas on that?

O2 sensor replaced some slight improvement but still shaking in gear when stopped, or under electrical load (A/C, lights)

Someone mentioned engine harmonic balancer?

Thanks again. Going on 4 months with this...

What is the idling speed when stopped and in gear? It could be due to bad engine mounts.

Low rpm when cold and increases when hot indicates the ISC is not working correctly.

MAP if equipped would be at thw firewall, with a vacuum hose attached.

Last mechanic just jacked the idle adjustment to hide vibration i suspect he had it at 1k+ Mounts are new. So I reset the idle by ear (500?) the ICS reset and I got high rpms on start then drop (normal/good) and noticeable rpm changes with ac and gear selection. Still vibrating but ever so slightly better. Then I pulled the neg batt to clear the CEL and noticed hunting/wandering rpms that did not self resolve after about 5 mins at idle as per manual. Vibration is almost gone while in gear and no a/c but returns w/ a/c on.

If the ISC is non OEM, I would suspect that as the cause. Try removing the cover plate and check the internal gears. If they are dry, get some di-electric greas and remove the gears to apply the grease. The gears could be sticking intermittently and when A/C is turned on, the rpm dropped. Get a tachometer to check the idling speed. Rm should be 700-800.

After disconnecting the battery terminals, the computer needs to relearn so the idling could be erratic.

Followed mfg idle reset - ISC reset and is operating. still vibrating in gear, can feel to a much lesser degree the same rythmic shake out of gear with ac. still shakes in gear with ac. although is a little better now. rpms are still a little wandering.

Check the valve clearances.

Had (supposedly) valves checked and adjusted. Could this be a gas cap problem? Mine is a little rusty with some crystallization but seems ok otherwise. It is the original cap.

When I give 15 seconds of ignition w no start then crank the ICS SEEMS to recalibrate meaning I get searching rpms again. Everytime it seems to search less and less. Should I just give it a week to try and sync? Someone also mentioned programming the (new ECU) any ideas around these two issues. Thanks again.

The ISC is faulty causing the problem.

ISC is new from mitsubishi. only a few months old. wandering rpms are self resolving but i am getting a little random rpm surge when stopped in gear post MAF replacement. vibration is still a problem still rough in gear at operating temp. something is not telling the engine to lean out? or increase rpms? while in gear at a stop. its almost backwards meaning out of gear no ac rpms increase and idle is smooth in gear w or w/o ac rpms increase a little but not enough? and i get a steady shake through the steering wheel - shake stops as soon as i'm out of gear. is throttle position sensor a possibility?

could use additional information on MAP location - but can not find it or any reference to it on 90 mitsu mirage.

That means your vehicle is not equipped with MAP sensor.
How many mounts did you replace?
What are the idling speed under each conditions as described?

Mounts are maybe 3 months old. Reset idle again by ear. The car wants and does for a moment, run smooth in gear but then shaking starts and exacerbates I also hear some puffing like exhaust leak ( but had that checked )as idle lowers and shaking starts most noticeably when I first go in to gear.

Replaced all 3 motor mounts and 1 trans mount. 3 months ago

Setting idle higher doesn't seem to help.

I need to know the idling ccondition. Setting it higher would cause more problem as the computer would be compensating for too low rpm and decreasing when it gets too high.

By ear? OMG, so the idling surge is by ear too?

I know. The idle surge has resolved / is gone. Suggestions to read RPMs? I have no tach installed

You lost me there. I am confused as to the problem you are facing now. You mentioned surging is gone but then you have intermittent surging which you are only feeling because you don't have a tachometer. For accuracy, you would need to install a tachometer or at least attaceh one for testing. There are clip-on tachometers availble at parts outlets.

Btw 3 months though not too long is enough for engine mounts of inferior quality to fail. One thing that can cause this is a bent center support. When this support is pushed upwards, it would cause vibrations as the front and rear mount would be compressed. Have a visual check and ensure they are not compressed. Removing the center bolt of the front mount would allow you to see if front and rear are aligned.

Your last comment might be the answer. Even though the mounts were bought from RockAuto less than a year ago the vibration never resolved. I can see the engine "jump/move" more than an inch when in gear and out. Does this sound like a bent center support? I have not inspected it lately but will tomorrow. It did take some muscling to get the front mount in and adjusting to get it to line up.

This problem manifested itself one day years ago. It just appeared. It was mom's car perhaps she did hit something or run over something.

The only other weird part to this is that when the engine is cold there is no vibration in gear. But as soon as it reaches operating temp the vibration is there when in gear. I am also noticing a tough start in the morning, the engine idles very low and then the ISC kicks in and rpms come up - but not right at start up.

Thanks for your continued advice/support.

The only other weird part to this is that when the engine is cold there is no vibration in gear. But as soon as it reaches operating temp the vibration is there when in gear. I am also noticing a tough start in the morning, the engine idles very low and then the ISC kicks in and rpms come up - but not right at start up.

Yes, I believe the center support is damaged since you need to force the front mount in.

When cold, the engine would be running at a higher rpm due to the cold start feature so vibrations might be minimal but when idling speed drops, the vibrations would increase.

During cold start if the rpm does not increase immediately, it could be due to a dirty ISC. The other thing would be the valve clearances. If they are too tight, the engine would idle slightly rough and that might cause the vibrations and the
low idle at initial startup.

Please see the attached video pics. I can not tell if its "bent" or not but obviously took some damage. Re Center Support - is that, scratched, rusty bar running font to back it? The front of the car is to the right of the screen.

I suspect the ISC is dirty / other since I have pulled it, connected, unconnected, reconnected it many times. Suggestions on cleaning it?

I did have a guy adjust the valves - I believe he got creative on setting them to resolve this problem-to no avail-do you suggest another valve adjustment/job? The car does run rough (quite) at cold start up, and will stall if I drop it in to gear, if the ISC has not engaged.

Would additional video help nail this down? Im pretty sure we've got it ID'd but would like to be quite sure before I drop it off for another attempt to resolve.

Thanks again.

I can't determine anything from the pictures so am not able to make any comments.

Well Im stumped. I replaced the center brace, got the ECU rebuilt, replaced all fuel injectors, timing belt, had valves looked at and anything else I could think of. The good news is the ECU rebuild fixed the ISC fail/sporadic behavior. The rpms are high at cold start up and adjusts as the AC compressor kicks in and out and temp comes up and I have no vibration in gear. But as soon as the engine is warm the vibration in gear is back and is exacerbated as AC,lights,brakes or steering are engaged at normal op temp. It idles smooth as silk out of gear and warm but starts vibrating in-gear under any kind of load but only in gear.

Ive notice the head lights dim as AC is put on when in gear. Idle has been set with code scanner (no code - no check eng light) to factory specs.

Could it be a sensor or switch in the gear selection housing? Or the alternator? It happens in every gear and I mean as soon as I shift into a gear (auto trans). Sometimes it smooths out a little - usually when the AC compressor kicks in or if I put it on a high setting (more blower) and rpms come up.

Engine temp sensor checked out ok. The only other thing Ive noticed is despite a new thermostat the temp gage still shows the normal op temp running a little above the normal hash mark. I am at a loss for what to do next. Thanks again.

I believe the engine mounts are bad. Check the ones at either side of engine compartment, timing belt and transmission

That (mounts) was the first thing I did in April of last year. I just replaced two more this week with no improvement.

Which 2 were recently replaced and were the mounts allowed to settle down correctly before they were tightened?

Did you check if the front and rear were installed in the correct direction?