Small throttle opening causes erratic RPM

[respley]

I have a C280, (Engine 104.941) with an odd problem. At low throttle levels in park, the engine RPM oscillates between 500 and 1200 RPM. This causes problems when driving as when I go to drive away, the RPM drops off then suddenly picks ups. Besides this, no other symptoms, idle is stable and other driving conditions show no symptoms. Any ideas?

Check to see if you have a code set. I expect the problem to be in the area of the Idle control solenoid or a possible vacuum leak.

Good luck,

[respley]

I've had a look around the www and could not find out how to read the codes. I found plenty of information on OBD1, OBD2 etc but i'm not even sure this vehicle has this in place? - confused!

[smharr4]

Originally Posted by respley

I've had a look around the www and could not find out how to read the codes. I found plenty of information on OBD1, OBD2 etc but i'm not even sure this vehicle has this in place? - confused!

If your C280 is a 1996 or 1997 any auto parts store will let you borrow/loan an OBD-2 code reader, the OBD-2 connector should be under a flap close to the steering column. You should be able to purchase cheap OBD-2 readers from the same place, it'll come in useful.

If it's earlier than 1996, then you'll need to read codes from the small black box near the battery in the engine compartment. The pre-test conditions, method for reading the codes and what they mean should be available if you search these forums (my car has one of these boxes).

If your car is older than 1997 I'm surprised it has an M104. I thought the M112 went into MY1998 and newer C280 W201's.