92 500sel idle problem
 

Hi everyone. Just bought 92 500sel. Idles good when just started then It goes up and down. Will idle good like 650rpm for 30 seconds sometimes longer then it drops car almost stalls then idle goes up to 900rpm then back to normal. Any ideas what it can be? Thank you
Victor

Its got a idle speed matrix, to speed up the engine when things are running, like AC, an load on the power steering etc. It is mentioned in the service CD. For starters get yourself the MB service CD, its $160 and covers wiring and trouble shooting 92-99 and owners manuals.
The car has sort of an electronic accelerator, dont move the linkage under the hood by hand while it is running, I have been told it will go into limp home mode (very little power from accelerator).

Might also be the MAF sensor. Insulation on the wiring in these cars go bad after time. Check out the link below. It's specific to a V12, but the problem is the same...

http://v12uberalles.com/MAF_rewire.htm

thank you for help. my cam advance solenoids wire insulation falling apart. its all cracked and falling off wires leaving them exposed and shorting. i think the rest of wiring is in same condition. i have to check throtle actuator wires. thanks

sometimes it is carbon buildup on the EGR valves that causes rough idle. my 97e420 idle fluctuated slightly when cold. i noticed that when idling the rpm would go from about 650 to 500 and up again but i don't notice that once the car warms up. my car has 152k miles.
if it is carbon deposits then the only way is to take the head top off and manually clean the valves.