hey i have an 89 5.0 tbi engine and with the a/c off it runs perfect but when im at a light with the a/c on it idles like at 500-600 rpms and its a lil rough what can it be?

 

Well, the ECM should be compensating. There are target idle RPMs in the ECM. One with AC on and one with AC off. Have you done any chip tuning or messed with this at all? If the signal is not reaching the ECM to tell it that the AC is on then that could be your problem right there...

Later,
Harry

 

If you've got worn out ignition components, wires plugs module cap rotor coil, then when the ac turns on and the load on the motor increases the idle will drop but since the ignition components are worn out then the spark is not hot enough to maintain the lower idle and the ECM is attempting to componsate with more fuel/IAC adjustments to prevent the motor from stalling. Thus causing the missing/sputtering/surging you are likely expierencing.

Even if you test some of the ignition parts and they pass a test they still might be worn out. I suspected my module was bad but I had it tested out just fine. I replaced it anyway and when I did all of my idle problems disappeared.

 

my car is complety stock so you said the module cloud be it oh well when i get some money i will replace it or take me car to be check

 

There is a wire from the computer that gets power when the a/c is on. That could have been disconnected or broken.

Charlo

 

what color, or were can i find this wire to see if its broken or disconnected?

 

I believe it connects to the the + for the a/c clutch. Not sure, Ijust know my painless wiring kit came with one for my 7077. Says to connect to positive for a/c clutch I think.

Charlo