[pzwestside]

I have a 1989 Ford Mustang LX 5.0, and have noticed that when the A/C is turned on, or the fan in general for heat/cool, the RPM's drop to 500 when idle, and eventually craps out on me.

Does anyone know if this model of the Mustang should be only 600-700RPM when idle? I was under the assumption that it should be around the 800-900 marker..

Can anyone help me in regards to this? and how I may fix this problem?

[GhostDog 5.0]

Raising the idle should take care of it. When you adjust the idle bolt on the underside of the throttle body, you need to adjust your throttle position sensor voltage to 0.98v with the ignition to the on position but the car not running. The green colored wire provides the voltage you need to read. To adjust it , you loosen the screws on top of the throttle position sensor on top of your throttle body and rotate it left and right until the voltage is correct. Your idle may change after setting it so you may have to go back and forth a few times. My 89 idles at 650-700.

[tmoss]

The Idle Air Bypass (Idle Air Controller) should make up for the A/C being on. Have y0u cleaned it REALLY good lately. They can be hard to clean completely.

[1stPny]

I had the same EXACT problem. When car was warmed up I noticed it.

My cure to fix it.

1. Clean the IAC, MAF, TB, Upper Intake, K&N. (problem occurd about 50% of time)
2. Got an "Engine Idle Air kit" (FORD PN F2PZ-9F9S9-A) ( major improvement problem occured about 25% of time.)
3. Checked TPS and it was between .31 and .53. Could not fix. Got a new one.
4. Installed new TPS and problem has not arose since.

By doing all this the time span was roughly 1 month. Except the IAC "spacer/adjuster" and the TPS which was about 2 days. I hae also noticed an improvement in Fuel economy as well.

[pzwestside]

Thanks for all the input, I will try these and let you guys know.. I appreciate the response..