Greetings,
Someone in this forum had said "Welcome to Mercedes, fix one thing, another breaks", boy he was right........

As you all know I had huge problems with my idle control system and finally the idle control unit fixed all of them, then the car started to overheat so I am pulling the radiator and taking getting it fixed.

Now I took the car to the mecahnic to do the fuel/air ratio adjustment as I messed with it while I was diagnosing the idle problem and he said the ratio was stuck at 50%.... Meaning that o2 sensor or Engine Control Module or Frequency valve wasn't working. And told me to check it...... My stupid $120 manual gives no information about how to check any of those things, but it does tell you what they do and where they are at (except I can't figure out where the engine control unit is at).

please help again

The engine control unit I assume you mean the computer or Electrinic Control Unit ECU as it is often refered to is under a plastic cover, which is under the forward portion of the pasenger side carpet.

And I disagree, when these cares are fixed right they are bullet proof.

Good Luck
John Roncallo

Do you have any testing instructions?

If I ever get it fixed I'll let you know.

...or they coould be referring to the Ignition Control Unit which is bolted behind the driver headlight on the wheel well. These are routinely available on eBay for a decent price. As with any used electronic part there is risk in buying one off eBay, but I've had pretty good luck with the spare parts I've purchased.

__________________
Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000

No, I was talking about the ecu.

Try this link

http://www.landiss.com/mixture.htm

Also known as the lambda control unit

Well I put the radiator back in and the car started to idle normally again like the lambda system started working... I did notice that the relay for the lambda system was very hot, but it was functional as I swapped it with the fan relay and the fan continued to work. So if the relay was shorting out that problem is fixed or I will see it with my fan.

To continue the test (keep in mind the car is running perfect) I grounded the o2 sensor to the frame and the car started to idle a lot rougher, then as I plugged it back in it went back to normal.

I found the lambda system (keep in mind the car is still running perfect), unplugged it and started the engine and it started missing and sputtering just like the day it was at your shop. Then I shut the car off, plugged the lambda system back in the car was running good again.
Here is the par#: 002-545-0032