Idle very rough when cold
 

I have 1989 230E, 8v. It has mechanical (KE*Jetronic) fuel injection that works the same as in 300E model cars.
Everytime when starting at freezing cold weather the car starts up in a second idles nicely at 2000 rpm for 2-3 seconds, then idle suddenly drops to 500 rpm, engine starts idling very rough and sometimes dies. As engine heats up the idle rises to 750 rpm and starts idling fine. When starting with the hot engine car starts, idles at 2000 rpm for 2 seconds, and then at 750 rpm constant.
I watched the current to the idle valve and saw that it gets 12 volts (opens up, makes click) as soon as I turn on the ignition. If I dont' start car in 10 sec voltage drops to 0 volts and it again clicks. When starting the car idle valve gets 12 volts for 2 seconds, then it gets 0 volts and 0 milliamps even if the car is idling rough at 500 rpm.
Almost same thing happens to EHA. It gets constant 20 milliamps with ignition on, 30 milliamps for 2 seconds after start and then 0 milliamps afterwards.
My car doesn't have starting problems but it looks like the computer quits working in 2 seconds after start. So far I checked idle microswitch, throttle position sensor and temp sensor. They seem to be working corrrectly and there is voltage at their pins. The only problem is the air potentiometer which I have disconnected for incorrect readings and causing of surges.
My questions are:
What should be the engine's idle speed when started at cold about 0 celcius (32 Farenheit)?
Why is my idle valve clicking(worlking) at ignition on engine off and quits working after start?
Someone please explain.
Thanks for reading,

Hurshi

The airflow sensor is essential for closed-loop electronic control, i.e. the EHA and the idle control valve. If you have it disconnected, then the computer has no way of knowing that input info, and it is reasonable it will produce no output. Since a start condition will not produce reliable inputs, some default parameters are necessary for this condition. The controls would be expected to look for closed-loop feedback as soon as the engine is running. If your airflow pot is bad, replace it before attempting further closed-loop diagnostics.

Steve

HURSHI

I HAD THE SAME THING HAPPEN TO MY 89 300 SEL. I WAS ON A ROAD TRIP IN THE MOUNTAINS WHEN MINE STARTED. IT WAS MY AIRFLOW SENSOR, NOT A CHEAP PART. I DID TRY THE IDLE CONTROL VALVE, THE TEMP. SENSOR AND EVEN THE COMPUTER FOR THE INJECTION SYSTEM(I WORK FOR A DEALER SO I DID NOT KEEP ANYTHING I DID NOT NEED), NOTHING WORKED. BUT A TECH CHECKED IT OUT AND APPARENTLY IT HAD A BURN MARK ON IT THAT AFFECTED THE IDLE. MY CAR DID EXACTLY WHAT YOURS IS DOING. NOW IT WORKS PERFECT.


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