Idle Problem
 

When I run the AC or heater my idle goes up and down from 500 to 1500rpm a few times then eventually dies. Now, the other day I was driving along without the AC and it just died on me! I have replaced the Idle Air Control Valve, the TPS, and the MAF is clean. Any ideas? All this started before I ever made any upgrades, and it's still going on.

Re: Idle Problem
 

Well, you have checked all the usual suspects. Sous to me like your base idle is set too low and the idle is hunting. The problem will get worse with the AC running.

Here is how to fix it:

1 - Start the car.

2 - With the motor running, unplug the wire harness to the IAC. If the car dies, you have found your problem.

3 - When you unplug the harness, the car should almost die, but not stop running. If the idle is unaffected by removing the harness, then the idle is set too high.

4 - Adjust the idle set screw on the TB until the car just barely runs with the harness removed.

5 - The SES will come on...no worries. Disconnect the battery to reset the idle speed fuel curves and reset the light. Reconnect and you owe me a favor! If this does not work, then sell it. :D

Re: Idle Problem
 

If your AC is low on refrigerant it can contribute to the idle going up and down too, but it wouldn't cause the other things you are seeing.

Re: Idle Problem
 

IAC's can be cleaned by removing and spraying with carb cleaner. That sometimes helps to stabilize the idle..........

Re: Idle Problem
 

Bob, this is one of those "usnusual" problems...but it sounds to me like a bad solenoid/sensor somewhere. I would OBD2 scan your EEC and then work it from there, heres some of the codes you may find:

http://www.allfordmustangs.com/Detailed/445.shtml

There are too many things that could cause your problem...