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My 91 GP wont idle below 1100 RPM?

C

carnut

New member
My 91 Grand Prix is a 3.4 with 5 speed Getrag trans. as the title says, it will start cold quickly settling at 1500 RPM for about 2 minutes, then drop to 1100 RPM and stay there. It has a cleaned throttle body, replacement of the Idle air control valve (4 times!) Verified throttle cables have slight slack. Backed off the minimum idle screw with no change. I confirmed the dash Tach reading with a hand held RPM tach/ dwell meter. I've checked the vacuum hoses that I can get to without removing the upper intake. They are either new or intact and secure. In all other respects, this car runs great. Good power, smooth idle and it gets to temperature (195 F) quickly. What's left?
 


spray the vac lines with carb cleaner, if the idle jumps up higher you found the leak area. move the lines while spraying if it dont show its face right away.
 
I had a 91 park avenue that wouldn't idle below 2,100 rpm. Turned out that the throttlebody was so gunked up with carbon build up that the previous owner adjusted the throttle plate to open more at idle that after I cleaned it the sludge gone it would idle that high.
 
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