Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi, and welcome back. It's probably best if I call and talk with you about this on the phone. If you will accept the additional service offer for the phone support I can call you tomorrow and help you with this.
Okay, the first thing I need to know is whether the rpm increases to 1500 rpm when you disconnect the idle valve. I believe you mentioned that it did not increase.
Okay, do you know how to adjust the fuel mixture?
You need to adjust the mixture for highest engine rpm. Click on the attachments below.
When the car is idling high I would suspect a fault with the idle control unit or the overvoltage protection relay or the connections to the idle valve. First I would tighten the connections at the valve. Next you would need to remove the cover on the back of the connector on the idle control unit so you can probe the terminals for power when the car is idling high. You should have 12V on the red/blue wire at terminal 2. Power comes from the overvoltage protection relay. If you have no voltage you will need to replace the relay. If you do have 12V when the idle is high I would replace the idle control unit. I've also found that poor connections at the control unit can cause erratic idle speed.