AC problems

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Aug 17, 2008
Southern Oregon
I really needed the AC today which previously worked very well last summer but today when I pushed the button in the RPMs went up and down from 1500-2000. I could also feel the gas pedal depress and come back up over and over. Not really a big deal while driving but while at stop lights it was a little strange. The AC seemed to blow cold but just revving the engine on its own. Any ideas whats causing this and how to fix it? Thanks - Jesse
i take it thats it is an automatic so that beening said it has an idle adjustment to boost the idle to compastate for thr drag from the compressor. check around the intake maybe you have a bad vacuun line and its not holding vacuum and the idle is jumping because of that
No, its an 87 manual. Sorry the RPMs are from 1000-1500 back and forth while idling. I have been chasing a vacuum leak problem and found one at the vacuum advance on the distributer that solved a hesitation problem but I think there might be smaller leak somewhere else as it still hesitates from time to time although nowhere near a bad as before.
The idle up diaphragm is mounted on the front of the carburetor. At the bottom front where the diaphragm linkage attaches to the primary throttle shaft is an adjustment screw. You can turn the screw out to reduce the rpm. Because the diaphragm is vacuum actuated, if the idle up rpm is set too high, then the rpm surges up and down.

Of course you should try and fix your other vacuum leaks, but this screw could just need a little adjustment.

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