It starts to idle rough and hunt (RPM's increase and decrease continuously) when I turn on the AC or the defroster. Could a bad ground be the cause of this?

 

Could be something with the AC compensator circuit. I'm running a commander 950, so i'm not too sure about the stock ciruitry (how it goes to the IAC). I have the holley harness too.

 

The rear defrost takes a lot of current, so it puts more of a strain on the alternator to keep up the charge; hence it loads the engine up a bit.

Pete

 

Were you talking about the rear defroster? I was assuming the front, since running the front defrost automatically kicks on the AC compressor, which is why you get the same effect from turning on the AC or the defrost. If just the rear defrost was enough to drag down the engine, i'd say you had a wiring problem.

 

It's not the rear defroster, it happens when I either it on defrost heat or defrost AC.

 

when u move the lever to the defrost position, it kicks in the AC compressor clutch, no matter what temp setting u have it on. It does that to dehumidify the air, making the defrost more effective.
That's why i said AC compensator circuit. Have u checked it at all?

 

Thanks for sending me in the right direction, do you think by changing the AC compressor it would help? I have a spare one, it shouldn't be hard to change would it?
Thanks alot

 

If it was anything in the compressor, it would be the little switch that sends a signal to the ECM to trigger the compensator circuit to kick up the IAC. Should be a little round connector, depending on the year. unplug it and check the switch with the mulitmeter to see if it switches when the clutch kicks in. the switch should be retained with a little internal c-clip if it needs to be changed.

 

I'll check it on monday while I am in the shop. I am surprised I got a response for this problem, I figured it would be a very hard one.