Thread: rough idle

my idle is really rough. The car shakes and the rpms go up and down rapidly at idle. Black smoke will come out of the exhaust and it smells. The car gets to the point where it sounds like its going to cut off. However it accelerates and drives fine and smooth. This happend after i had the battery out of the car for a couple of hours. Any ideas whats wrong? 1999 grand prix gtp

it was on. one of the codes was egr valve stuck open and the other was the maf sensor. So i replaced the sensor and the codes went away but still no luck.

i took the top part of the egr valve off and cleaned that. and i dont think its the maf sensor because i put a brand new one on yesterday.

yea im saying i did have a bad maf which threw a code. so once i got the code i switched the maf with a brand new one and the code went away. but once i switched the maf the car still had a rough idle.

Check the vacuum line going into the side of the throttle body and trace it back to where it goes. I replaced my thermostat and pulled this line off the side of the throttle body to move it out of the way. When I buttoned everything up and started the car it did the exact same thing. Slide the line back on and all fixed. Yours may be cracked or the hard plactic line might be broken further down (line runs along the front of the UIM).

put all new vacuum lines in. the idle isnt as rough but its still rough. i looked at the exhaust pipes and water was dripping from them