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Why would a 1992 Sunbird GT die when applying brakes and also revs up and down in a cycle?

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2015-07-17 17:39:42
2015-07-17 17:39:42

Hey Pete==Have the brake booster checked out. The diaphragm may have a leak. GoodlukcJoe

just took it out for a test drive and it only happens when car is at operating temp not when cold any ideas?

try flushing out the fuel system. stuff builds up in there and it doesn't run as clean and as well as it should. also anylost power the car had wil be restored and your gas milage should improve. i have a 92 and it did the same thing


HeadlineIt's either a vacuum leak (check all hoses) or it's probably the Idle Air Control Motor (or IAR it's sometimes called) needing cleaning. These cars and other J-body cars too, are known for this problem, in fact not just GM cars either. My 92 3.1 V6 Sunbird does the same thing about every 5000-6000km, maybe even less. It's a little motor (usually black) with a 3 wire connector on it right near the Air Filter hose and throttle body and it has 3 vacuum lines in a row coming out the other side of the plenum it's attached to. A Haynes or Chilton manual will not show you the location of this motor and when you look it up and it usually says to take it to a mechanic because it needs to be hooked up to a computer. It doesn't in most cases (just disconnect the battery and reconnect when job is finished to reset the computer so it can "re-learn".) Use degreaser or Isopropyl alcohol or lighter fluid (something powerful that evaporates) there is a special spray too that my mechanic uses, anyway, submerge the motor, and don't worry about submersion it's a sealed motor anyway, shake out the excess (you'll see how dirty the excess fluid is.) wipe off and let cleaner evaporate/dry (unscrew the pintle and spring before cleaning so the cleaner gets right down in there, clean the spring and pintel too while your at it). Then reattach it to it's plenum (make sure to put the rubber O-ring back onto the neck of the motor)! If that doesn't work, take off the plenum the motor came off of, clean it and put back in with a new paper gasket (the original one is plastic and tends to get brittle from heat, mine broke apart in my hands after removal). Line the whole gasket with a thin layer of high-temp silicone for a good air-proof seal. If the motor is faulty (you can test it by unscrewing the motor out of it's plenum and turning the key, then turning on the air conditioning. A/C causes the pintel to move in and out, although I guess anything requiring more air like revving the engine would work too. if it's faulty, get a new one, they are usually only about $20. Don't worry if it does this "erratic idling" a little again at first after cleaning, the computer is just re-learning and adjusting accordingly. You will notice (on the RPM needle) that when the idle goes wacko again, the computer and motor together will "flick" the RPMs back down to where they are supposed to be (I use the word flick because the needle will literally snap back to about 600-800 rpm when the engine starts to rev. to high or too low). This is how you know it's fixed. After the computer learns for a few drives and finds a happy medium, your idling at a stop light or when applying the brakes should be perfect. The only difference between this method and a mechanic is there is almost no computer re-learning (they adjust it to the happy medium by computer instead of letting the computer retrain itself.) The main thing is the little motor is clean and that's the most important part. (Well, for a little while anyway, till it gets dirty again!) Isn't this what air-filters are supposed to filter out? :)

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