intermittent VERY rough idle...

[stlgrandam02]

hi, most of the time, my car runs like new. however, sometimes, when i start it, the RPMs go up and down while idling from 700 to 300 and back over and over.... if i shut 'er down, and wait a few minutes it usually starts up and runs strong. i don't know what the deal is, the lights dim when it happens too, which led me to believe it was a battery terminal problem, but no.... all that checks out fine. i had a problem like that with my old 87 plymouth acclaim and it was the terminals so i thought that might be it..

i also noticed the original alternator is still on the car (at 84k miles) i'm gonna have autozone test it. we also have new spark plugs and wires we're gonna put on it. we'll see what happens. does anybody here have any other ideas on what it might be? perhaps faulty ignition?? please help me, i just got this car and i want to make sure i keep it running strong!

i hope i didn't get a lemon that the previous owner drove the living shit out of. :(

('cuz i was plannin to do a little of that occasionally myself lol... and i wouldnt want to hurt an engine like that if it's already taken abuse, so i've been taking it really easy on the throttle since that started happening... well, i did smoke a fartcanned honda today tho... thats so hard to resist hehe)

NOTE: it's the 3100 SFI V6 if that helps. i know you people here know alot about this stuff. please help!

we had a 94 corsica w/ the same engine and that thing ran flawlessly past 200k miles, so i thought this would be a good one.

EDIT: oh yes, and we just put on a new fuel pump and filter, btw

-Mike

[Pickelicious]

I experienced this on my truck, and it turned out to be a vacuum line had come off. It could also be your Idle Sensor, I believe that is on the throttle body. Would be worth trying changing that out, they don't really cost that much.

[Texican]

Originally posted by Pickelicious
I experienced this on my truck, and it turned out to be a vacuum line had come off. It could also be your Idle Sensor, I believe that is on the throttle body. Would be worth trying changing that out, they don't really cost that much.

Or remove it and clean it with sensor safe throttle body cleaner and brake cleaner to rinse it. The Idle Air Control (IAC) should be inside the throttle body, under the IAC sensor.

[rixGAphx]

A prime candidate for loose vac line is the 'Tee' connection about 6 inches from the vac bottle.

The vac bottle is plastic, about the size and shape of a small Nerf football.
It resides under the battery tray. Its nipple points straigh into the engine bay, and it's easy for the connection to the 'Tee' to be dislodged.

Good luck.
-Rick

[Silver99SE]

Ya definitely check the vacuum hoses. The same thing happend to me years ago when I had an Oldsmobile with the 3800 in it. It even went so far as to quit when I put it in gear. Turned out to be a BIG vacuum leak.