Rough Idle, '96 Regal, 3.8L

[The_Cams]

Hi all,

My 1996, Buick Regal, 3.8L, series II, 165,000 miles; has recently began to idle roughly. I'm hoping someone has some ideas to help me fix this.

Symptoms: Rough Idle. When driving everything is fine (smooth as can be). When I get to a stop sign or light and have to stop - rough idle again. It's a bit better when the car warms up. Misfires (cylinder 3) at start up every morning. It's been rough for about 3 days - just started.

Haven't noticed any significant loss in mpg.

Codes: misfire in cylinder 3 (over and over - only at idle).

Ruled out: Plugs, wires, and coils are fine. Vacuum off manifold is low at 15, with a slight jiggle on the guage.

I replaced the UIM, and LIM gaskets in the spring of 2007. Mainly preventive, they were not leaking. I'm thinking maybe the UIM gasket has an air leak, but how do I pin that down? The other vacuun lines looked ok.

Any ideas would be appreciated.

[wjcollier07]

how you know the wires are fine?

i'd personally start with running a good concentrated mix of seafoam in the gas and through the intake.

i definitely wouldn't rule out LIM gasket...could very well be some coolant getting in there.

[The_Cams]

Hi,

Thanks for the reply.

Swapped s.p. wire from cylinder (3) with known good wire and ohmed out both - they're good. Recently (3 months ago) changed the front plugs/wires. I still have to get to the rear plugs/wires (they have 70K on 'em). Since the consistent code is a misfire on cylinder 3 - that's where I focused. Changed that plug too.

Did the spark test on the coils, they all spark (one at a time when unplugged) with IAC unplugged, and engine running.

I'll probably bring it to the dealer in the morning, as I don't have a lot of time to mess with this. Maybe they can point me in the right direction. I'm thinking a manifold gasket for the plenum. Hoping it's not valves.

[The_Cams]

All Fixed Up!

The culprit was a leaking o-ring on a fuel injector.

Popped the fuel rail, put on new seals - good to go. No more misfires, runs like a champ.

[bill buttermore]

Thanks for posting the fix. It will help others. Please consider adding "fixed" to the title of the post to make this information more valuable to those searching for solutions to idle problems.