I'm going through the troubleshooting of a high idle on an 85 500SEC.
If I pull the line to the vacuum-advance on the distributor, the idle goes back to normal. This is not the solution, however.
I am going through the troubleshooting sequence in the M117 manual to get to the bottom of it.
What is a safe cleaner for vacuum valves? Some have suggested carb cleaner, but there are rubber parts in many of them, not to mention vacuum hoses don't like solvents. I'd guess that spraying carb cleaner down an ICV will kill it.
I pulled the ICV to make sure the valve was free inside, but haven't checked all of the voltages yet.
PB Blaster and Deep Creep seem to be safe for electronics and air intake systems. Is it a bad idea to get penetrating oils into vacuum systems? It's never caused me a problem before on rubber or plastic etc.
Idle control seems to be one of the most common problems with these engines.