idles at 500 rpm with compressor running...

[jdSHO94]

i have a 1994 MTX and i have had this issue intermittently since ive purchased the car- with the climate control on any setting that uses the compressor the engine idle drops to 450- 500 RPM and wont compensate. Has anyone else ever encoutered this before? otherwise the car idles fine and behaves normally- not being able to use the defroster when sitting still is beginning to get frustrating.... any help or input would be greatly appreciated.

 

[jedhead]

Have you reset the idle?

Bob

 

[SHOZ123]

Sounds like a bad IAC/IAB as the PCM should increase idle speed as the compressor comes on. Could be a bad input into the PCM too I guess.

The idle should easily re-learn itself within a day of driving.

 

[jdSHO94]

ive tried resetting the idle 3 times now to no avail. It seems as though the IAC is operating correctly ( and besides that i replaced it about 3 months ago) it just doesn't "see" the compressor load.

 

[projectSHO89]

....it just doesn't "see" the compressor load.

In that case, run the KOEO test both with the A/C on and off (prescribed setting). You should get a fault code with it on but not with it off.

This will test the input to the PCM that is used to detect A/C system operation for idle load adjustment.

You might also have a vacuum leak....

Steve

 

[SHOZ123]

Another thing to try is to open the TP a bit with the throttle stop screw. This will give the IAC more headroom if it were to be near maxed out.

 

[jdSHO94]

ok ill give that a shot thanks guys!