Can sludge in the carburetor cause racing?

Dear Car Talk

Dear Car Talk | Dec 01, 1990

Dear Tom and Ray:

I own a 1983 Olds Cutlass Ciera. When I have the air conditioner or the defroster on, the car will start racing. Really racing! I can have my foot on the brake, and you can hear the gas pedal clicking by itself. If I turn the A.C. off, the car immediately returns to normal. I've heard of other people with the problem and their only solution was to disconnect the A.C. My mechanic thinks it might be tied to the computer. I asked another mechanic and he thought it was sludge floating around in the carburetor. What do you think?

TOM: I think there's sludge floating around in that guy's brain, not in your carburetor, Chris. My guess would be that your idle speed control isn't working properly.

RAY: The idle speed control is SUPPOSED to raise the engine idle when you turn on something like the air conditioner. The air conditioner takes a lot of power from the engine, and to prevent the car from stalling, the idle speed control is supposed to compensate by turning up the engine speed a little bit.

TOM: But when it makes the engine race excessively, the idle speed control is probably malfunctioning. It may need to be replaced, or it may just need an adjustment.

RAY: The best place to take it is probably your Oldsmobile dealer. This is one of those repairs that's simple once you've done it a few dozen times, like your Olds mechanic almost certainly has. Good old Fred--down at Fred and Ethyl's Filling Station and Charm School--may be just the right guy for a tune up, a brake job, or some advice on etiquette. But if he's never done this repair before, he may have to charge you an hour and a half labor just to find where your idle speed control IS.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One