same problem different solution
This is a very good thread on the idle surge problems some of us are having.
My 1989 230E used to keep accelerating for 2-3 seconds after I release gas pedal. That was very a dangerous car to drive.
Interestingly when two months ago I have disconnected the electrical connection to the idle control valve and the car stopped surging . The car was surging because the idle computer was keeping the idle valve full open when surging(found this by monitoring the voltage to the idle valve). I think that the idle computer is reading false data from some sensor or switch. When I reconnect the idle valve the surging returns and idle goes down from 1100rpm to normal 800 rpm.
Right now I am driving the car with idle valve disconnected because it is better to have a higher idle than have the car accelerate by itself.
The so called "idle control computer" is actually called the Bosch KE fuel injection control computer. This computer:
-supplies EHA current and idle valve current,
-monitors the air mass meter, temperature sensor, idle microswitch, and EZL fuel octane corrector
-linked to the fuel pump relay, OVP
this is all according to the electrical scheme of the car I have on my pc.
Any of the above units can be a cause of the surge. It might be years before I find out what it is. However if we all think togeather and share our knowledge we can get to the problem faster than it seems.
Good luck everone.
1989 230E, 8v, 166.000 km, updated to 94/95 trunk & hood
2002 Daewoo Nexia 50.000 km
1987 VW Jetta GLE 16V, Recaro seats
1982 Volvo 240 DL (lovely car!)
and few more american cars.