horrible 3.1L idle

[dumbagain]

i've got a real bad idle in my 1991 3.1L cavalier 110,000 miles.
with the car stopped, tran in D, brake on, the engine seems to surge.
the RPM gage with will bouce back and forth with the oil pressure gage dropping when the idle bucks.
when its really bad you can actually see the headlights and such dim during the down surge.
the check engine light seems to come on quicker when i leave the car in idle, but it doesn't hold any codes.
this problem happens even after plugs and wires are changed.

one note: if i am stopped i put the car in N and the surging/bucking doesn't seem as bad (doesn't shake the car).

thinking it might be a fuel prob? maybe injectors? pump?

what do you suggest?

thanks
mikez cleveland, ohio

[TimRapp]

Sounds like it can be a number of things but I would first try the idle control regulator which is located just to the right of the valve cover and should have to hex head screws holding it in place,but I think your best bet is having a diagnostic test done on it.

[thecommi]

Yes, you can check the IAC (Idle air control valve) up on the top of the motor, to your right hand side, but also check all your vaccuum connections. expecially the ones around the MAP sensor (located on the firewall) and the one under the plenum. now there is a gasket under the plenum but since its just air flow you can reuse it. its like 8$ for a new upper plenum set if you really want to replace them. there is a large vaccuum hose coming from the upper plennum out towards the firewall that can go bad. becarefull of the plastic vaccuum lines that run to the fuel regulator so you dont snap them. start there and see where it gets you.