Low Rough Idle W/AC On

[Joes4x4Ranger]

Got me a new project you'll be hearing from me a bunch. I've got a 91 4 door XLT, 4.0 Standard Trans 93,000+. It idles smooth at 900 without the A/C on. When I turn on the A/C the Idle drops to around 500 and it "lopes" real rough idle.
Carbed rigs have a solenoid that manually bumps the idle speed up when the A/C is turned on, activated by power to the A/C clutch. What does this on the FI motor?
I did a MAF cleaning and got WAY better throttle response but did not fix A/C ON rough idle issue.

 

[btexpress]

You most likely have a problem with the idle air control valve. This valve is on the side of the throttle body, with a two wire connector. It may be sticking or inoperative, or is not being controlled by the PCM.

This valve controls all idle speed functions by commands from the PCM, similar but more controllable, to the idle solenoids on carburetors.

 

[Joes4x4Ranger]

How do I check the IAC? Unplug it or tap on it as in other posts? If its inoperative would the A/C OFF idle be smooth or rough?

 

[Turdle]

How do I check the IAC? Unplug it or tap on it as in other posts? If its inoperative would the A/C OFF idle be smooth or rough?

Although this example is on a different vehicle-it will be the same procedure--and the part looks the same--

try this and see if it helps

IAC valve cleaning

http://www.explorerforum.com/forums/showthread.php?t=84220&highlight=IAC+valve