ROUGH IDLE IN GEAR THROTTLE POSITION SENSOR OR IDLE SPEED

1990 Mitsubishi Mirage

Tiny

mhooper87

May, 16, 2012 AT 12:32 AM

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.

Tiny

KHLow2008

May, 16, 2012 AT 4:16 PM

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

Tiny

mhooper87

June, 22, 2012 AT 9:36 AM

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.

Tiny

mhooper87

June, 22, 2012 AT 9:49 AM

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

Tiny

KHLow2008

June, 22, 2012 AT 1:08 PM

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.

Tiny

mhooper87

July, 18, 2012 AT 8:39 PM

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.

Tiny

KHLow2008

July, 19, 2012 AT 6:46 PM

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.

Tiny

mhooper87

July, 19, 2012 AT 7:01 PM

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.

Tiny

KHLow2008

July, 19, 2012 AT 8:12 PM

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.

Tiny

mhooper87

July, 21, 2012 AT 12:25 PM

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.

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