1986 190E 2.3 16V has very high idle
 

I have a 2.3 16V that has an intermittent high idle problem. Every once in a while, the car would idle at 2800-3000rpms. Unplugging and plugging in the ecu will temporarily fix the problem. I've tested the idle valve, air flow sensor, eha, all sensors, micro switches, and components and did not find any problems. When idle is high, voltage from the ecu to the idle valve is at battery voltage. Also, not sure if it's related, but the lambda control will show to be inoperative when the problem is occurring. I've changed the ecu with an rebuilt unit, but it still has the same problem. Any ideas what i should check next? I'm still thinking we received a bad rebuilt ecu, but would like everyones input before i put in another ecu. Thanks for all your help. Thanks

Simon

I am not familiar with this car, my comments are based on my 87, 260E. How about the accelerator mechanism sticking so that the idle switch is not coming on ? Or the idle switch is failing intermittently ?

I doubt that it is the ECU itself.

I've been diagnosing my '93 2.3 for the opposite reason, the idle is too low when A/C is on and the car is in drive. I have battery voltage (12.24v) on pin 2 of the idle control valve, but not full ground on pin 1. If I ground pin 1, the idle goes real high.
When your car is running, what happens if you disconnect the power connector at the idle control valve?

If i disconnect the plug at the idle valve, the idle will drop back to normal level. Also, if i disconnect the air flow meter plug, the idle also drops to normal.

I would still suspect the Idle Air Control Valve. I would refer you to TheRev (www.190revolution.net) but it appears to be down for the count.

I know when I first start my 2.6 it'll idle at ~1000 then once i put it into Drive it'll drop to 650ish.

Your idle problem does it occur in just in Park? Or does the gear not matter?

gear does not matter. it's has a manual transmission, but when it has the problem, it'll do it all the time.