I searched this forum under "idle". Found lots of posts regarding wavering idle RPM's but none that sounded exactly like my problem.
The car's an '89 325is. The idle is stable as far as speed, but it's very rough. When I'm idling at a stoplight, I can really feel the motor kind of jumping around. If I turn on the A/C, the bump in RPM's is enough to smooth it out to where it feels 'pretty' normal as far as smoothness.
Off idle, the car pulls strongly throughout the rev range. It does get slightly less mileage than I think it should (16-17 mpg around town, no freeway driving).
There are no vacuum leaks. The dipstick, oil cap, and fuel cap all seal well. The car has new plugs, wires, rotor, and distributor cap. The O2 sensor has tested good, and the car is not firing off any faults.
I'm thinking it could possibly be one of the following:
Fuel pressure regulator
Idle control module
Idle control valve (just cleaned)
ECU
I need to open up the ECU tonight to see what chip the PO might have put in.
Thoughts? Experiences?
The car's an '89 325is. The idle is stable as far as speed, but it's very rough. When I'm idling at a stoplight, I can really feel the motor kind of jumping around. If I turn on the A/C, the bump in RPM's is enough to smooth it out to where it feels 'pretty' normal as far as smoothness.
Off idle, the car pulls strongly throughout the rev range. It does get slightly less mileage than I think it should (16-17 mpg around town, no freeway driving).
There are no vacuum leaks. The dipstick, oil cap, and fuel cap all seal well. The car has new plugs, wires, rotor, and distributor cap. The O2 sensor has tested good, and the car is not firing off any faults.
I'm thinking it could possibly be one of the following:
Fuel pressure regulator
Idle control module
Idle control valve (just cleaned)
ECU
I need to open up the ECU tonight to see what chip the PO might have put in.
Thoughts? Experiences?