need help compressor idel up switch

[fastback65chris]

I have a 1990 GT and when the compressor kicks on my idel drops 400 rpm. I'm pretty sure this is not correct and when the compressor kicks on my idel should go up to compensate for the compressor. When the compressor kicks off the idel goes back up to 800 and idels just fine. Does anyone know what part I might need to replace that controls the idel when the compressor kicks on or off? When you stang is ideling at 400 rpm it sound pretty damn cool but when your in bumper to bumper and its 110 outside it gets a litter annoying thanks for any help

 

[Michael Yount]

The idle speed adjustments for things like that are handled by the IAB solenoid. It's the small cylinder mounted at a 45 degree angle on the front of the throttle body. The computer directs it to bypass more air to up the idle speed when loads (like the a/c compressor) pull the idle speed down. If I were you I'd pull the diagnostic codes and see what they tell you. The iab may be bad, but it could be other things or a combination of things. In the meantime, you might try pulling the throttle body and iab solenoid off and cleaning them thoroughly. They're notorious for becoming clogged up with gunk from part of the pcv system (hose to the valve cover) and then not functioning like they should.

 

[jrichker]

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html