Rough Idle - '97 GP 3.1L

[StevePT]

Alright, I've just about done everything I can think of to smooth out the idle on my 3.1L, other than a top engine clean with some seafoam or the like.

When I'm in Drive, at a stoplight the engine has a steady but not harsh rough feel to it. The driveability of the car is perfect, it has plenty of power and does not stumble. There's just a slight vibration at idle in gear and when I put it in neutral, it smooths out and then only has occasional "bumps" in the idle.

I have replaced the IAC, spray cleaned the MAF and the honeycomb with throttle body cleaner. Spark Plugs have been replaced with AC Delco plugs. Wires I haven't done, but when I did the plugs they all checked out with good resistance levels. Throttle body was off when I did the upper intake gaskets about 10K miles ago, so I cleaned the carbon off the backside of the butterfly.

Anything else? This rough idle has only started to show up over the last year and it is very light, but definitely not smooth like it should be. Seems like it idles more rough when the engine is up to temp, but that could be my imagination. Regardless, it definitely smooths out when I put the car into neutral and it turns into a smooth idle with sporadic "bumps" in the idle (which is how it has always been for years).

[rickisrad]

I definately would have replaced the wires while you were replacing the plugs. All it takes is a slight arch and it will affect the idle. I had a rough idle and miss One day when it was dark out I had the hood raised checking the fluids and seen the my wire arching and everytime my car would miss I seen the arch.

[richtazz]

Did you check the resistance of the wires when they were hot? If not, I'd put a new set of wires on it before going any further.

[jjubeck619]

check your motor mounts

[jjubeck619]

pop your hood and have someone switch gears from park to reverse to drive and back. your looking for engine movemont while changing gears