Ruff Idle 3100 mystery

[blackbombshell95]

I have a 95 3100 grand prix. my car idles ruff while in drive. but in neutral it seems to be fine cause it idles at about 800 or so in neutral. While in drive the rpms go down about 100-200 or so. And when i hit the gas it hesitates a bit. but in the rest of the power band its fine..

sometimes it even tries to die but doesn't. I was thinking it was a sensor or something...

i just replaced my tps last week... i've been having this problem for about 2 months now.

[96Prix]

Is your belt tensioner still tight? Mine is bad, the idle fluxuates a bit, and it hesitates off idle. There's also a light ticking when it idles.

My car has all of the sudden developed another eccentricity. When I hit the brakes, the lights flicker and the engine seems to stumble a bit. It's quite dramatic at night. There is a noticable momentary dimming of the headlights. Seems reasonable that it could also be a side effect of a bad tensioner. Need to get mine changed. Had one in my hands, but returned it and got my $100 back when I found the exact same unit online for $43. Still haven't gotten around to ordering that one though.

[Bens71442]

3.1 rough idle mystery

Do you have access to a fuel pressure gauge/hose? (I'd first start by checking fuel psi at fuel rail) and rule a fuel pressure problem very 1st thing!

look for 35-47psi at idle....(these are the specs from GM for a 1996 3100V6).......anything below 35 (replace pump)

If you do this test, (get back with me on what you find)

my engine miss was going on since last Oct. new fuel pump fixed it......but only after I was lead down the primrose path, and GUESSED at a faulty ign module. $167.00 dollars afterwards, (still misses) checked fuel psi, low pressure, (new pump at $378 dollars/parts/labor).....car doesn't missfire anymore! (I'm happy camper again ) pissed that I threw almost $500 dollars at it though!

guess my exhaust manifolds on my 71W30 will have to wait another pay day to recondition.

--Bens71442

[blackbombshell95]

RE: 3.1 rough idle mystery

well i'm using a gatorback belt. i've had it on for like 10k and its already starting to make noises when cold. i do have FFP pulley. but i doubt the pully has something to do with it...

but i do notice that when my car bogs down the voltage drops at the same time... i am going to do a fuel test next week... i have a voltage gauge, thats how i'm able to tell my voltage drops when the car tries to bog down.