Mechanics

ROUGH IDLE IN GEAR THROTTLE POSITION SENSOR OR IDLE SPEED

1990 Mitsubishi Mirage • 100,000 miles

I have a rough idle only in gear and wandering / surging rpms. Ive replaced motor and trans mounts, idle speed control, spark plugs and ecm/ecu but no joy. Is it the throttle position sensor? Or transmission? I do experience some slip and odd shifts but only when all sensors are connected otherwise she shifts smoothly. I have no CEL.
Avatar
Mhooper87
April 16, 2012.



I would look for a vacuum leak. Have the intake system smoke tested to find it. Intake gaskets are common.

Roy


ASEMaster6371
Apr 16, 2012.
Some trouble codes do not trigger the CEL for older models so it is good to check for trouble codes.

http://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.


KHLow2008
Apr 16, 2012.
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.


Tiny
Mhooper87
Apr 16, 2012.
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.


Tiny
Mhooper87
Apr 16, 2012.
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.


KHLow2008
Apr 17, 2012.
Smoke test was negative. Maybe I led on to know more than I do. How do I perform code check via diagnostic method? Thanks!


Tiny
Mhooper87
Apr 17, 2012.
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.


KHLow2008
Apr 18, 2012.
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.


Tiny
Mhooper87
Apr 19, 2012.
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.


KHLow2008
Apr 19, 2012.
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.


Tiny
Mhooper87
Apr 22, 2012.
Page 1 of 5