coupelex

I'm having problems with an uneven idle on my 93 SC400. It revs a bit and drops below a stable idle speed, and it's bad enough that I have to use the pedal and sometimes put it in neutral at a stoplight.

I've read a few threads, but still don't know what to do. So far I've only cleaned the mass airflow sensor.

What should I try next? Is there a typical cause to this?

Thanks for the help!

90sGold

I also have a 93 sc400. From what I’ve read cleaning your sensor with tradition maf cleaner ruins the sensor. I’m throwing the code 31 for the sensor, and I have a thread on how it doesn’t want to run when it’s cold. Seems like these cars have an issue with this part of the car, I haven’t quite been able to get to the bottom of it yet on my car.

coupelex

This worked for me:

1. I cleaned the Mass Airflow Sensor with electronics cleaner.
2. I cleaned the Idle Air Control Valve and throttle body with throttle body cleaner, and oiled the two bearings on the IACV and the shaft.
3. I unplugged the battery for twenty minutes.
4. After about 20-30 minutes on the road, the idle stabilized and lowered to about 700-800 RPMs, and the check engine lights went away.

90sGold

That seems like a good start. I’m going to test my sensor tomorrow with a multimeter and see if it’s faulty since that’s the code it wants to throw.

coupelex

I spoke too soon. Now my car seems to hunt for idle at about 1500rpm, but then after a half hour it settles down. If it sits for an hour, then the higher idle returns.

I am still thinking it's the IACV, it just didn't seem to move as freely as I would expect.

tobie171

sorry created a new thread for my question