I have an '86 420SEL that revs to about 4000rpm at start and doesn't go down. I've replaced the Idle Control Valveand itstill idles high. I can't take it to the dealer, so hopefully somebody can help me out with this issue.

Any help would be appreciated.

Regards,
Allen

I've also replacedthe fuel pump cutoffrelay - part# 002 545 16 05

 

I can't help you, but I have a related problem. On my 1985 500 SEL, I replaced the idle control valve because of high idle RPM, and now the car will not start. Starter revs, but engine does not start. Could the valve be incompatible - it was sold as compatible for this model?

 

Hello Hannu:

I can relate to your situation except our 85 500 SEL is hard starting. Need to pump the gas in order to crank her up. Changed the plugs, put new distributor cap and rotor but to no avail. Read aforum at Mercedes-Chrysler to turn on the switch for 10 sec. and pump the accelerator once and turn it off for another 10 sec. before cranking it up again. It starts but blowing black smoke b/c its too rich.Do you suggest changing the fuel filter?
Am a weekend DIY warrior who relyon books and up to know, stillwaiting for a CD126 service manual from MBUSA.
Any and all technicaland professional advice will be greatly appreciated.

Hoping for the best,

Bien

 

Hello, there is a idle control relay also, it is located next to the brake booster to the left toward the center of the fire wall., there are 3 relays in a row there, the one closest to the brake booster has a red-orange looking cover and that is not it,it should be the relay next to that one, or the center relay, black and maybe 3 inches long, I cant remember the part number but that will fix your high idle problem on the 500SEL, however I dont know if that would be the same relay for the 420SEL but I will check mine at the end of the month when I get it home, its not here as I just bought it off of ebay and it has the same problem and will be the first thing I fix on the car. also check for vac leaks while you are under there.

 

My 420sel 1990 mercedes have a high idle and some times when I'm driven it cuts off! When I put it in park it idle high an cuts off and it shakes when I'm at the light or when I'm just at a complete stop. What do I need to do?

 

I checked I did not see the idle control relay. It's not next to the brake booster.