Originally Posted by alteredx

I am having a problem with my newly acquired 1988 560sl. The symptoms are a high idle at 1200RPM and sometimes minor idle surging when the car is in park or neutral. The car idles normal in gear and runs good. The economy pegs to the left when the engine is running idle but sometimes moves slightly making me suspect a small vacuum leak. When driving the economy guage often moves into the red with only subtle throttle increases. I pulled the idle control valve and noticed that it is very fouled inside with carbon and barely makes any noise when I shake it. I replaced the idle control valve but the symptoms remain the same. When replacing the idle control valve I notice that the 2 hoses that it connects to seem to be very hard and loose fitting. I have ordered replacements for them. I also notice that valve cover to idle air distributor hose is very hard and extremely loose and oil has leaked out all over the idle air distributor. I ordered a replacement for that too. I also pulled and inspected the idle speed controller module but I do not see any visible signs of failure. I ordered a replacement for that just in case. I still have not checked the over voltage protection relay because the fuse is so tightly seated that it will not pull out. I think that I will have to take the kick panel off to get a better reach since I can barely get my hand to it from the glove box. All other functions of the car work excellent.

Can anyone offer me any additional advice on correcting this idle issue?