high idle 84 500sec - PeachParts Mercedes-Benz Forum

t walgamuth · #1 11-10-2005, 09:31 AM

i have my 500 for sale. it has always ran really well. so a guy comes to look at it and when we go out for a ride i notice that it is idling too high (1600), running a little rough and shifting a little rough.
that is the luck.

so i figure it is a vac leak. we searched for a loose or cracked line, found one, and replace it. my brother says ok now it is idling at 800, and seems fine. i say lets check vac. it is aobut 17checked at the distributor. my indie says that is correct. so now i notice that sometimes it idles at 800 and sometimes at 1600. a little roughness but not much, and the shifting doesnt seem quite right.

any smart ideas out there?

for lack of any clear direction i guess we will clean all electrical connections to sensors and hope for the best.

tom w

bergmjh · #2 11-10-2005, 01:24 PM

Normaly the Idle control valve will stick open gummed up with carbon. I believe you have an electronic idle control system. Take the control valve out and clean with carborator cleaner. If you are able check the function of the valve by shorting 12 v battery power across the valve electrical terminals. The valve should move from open to closed position with a audible click. Reinstall and hope for the best. If cleaning does not work measure the voltage at the valve. You should get around 5 volts on one side and ground on the other. If not check the fuses and wires over to the idle control computer. Sometimes a fuse or power supply is the only problem other times a wire goes bad. Good luck. John

t walgamuth · #3 11-10-2005, 01:28 PM

thanks for the detailed instructions. unfortunately i dont have a manual for the 500. can you tell me where to look for the idle control valve?

thanks very much.

tom w