1987 420sel high idle/cold start issues
 

Hi guys this is my first post so bare with me...I have an 87 420sel with 300,000kms. It is idling around 900-1000rpms in park and 700-800 in drive. I've replaced the idle control valve, idle relay, ovp and vaccum lines have been replaced, yet it still wants to idle a little high. Also in the last few weeks the car is hard to start when the engine is cold, it cranks 5-10 seconds before it starts, then takes a few seconds for the idle to smooth out. It only does this when cold, once the car is warmed up it runs fine, it doesn't stall or run rough and i don't see any smoke out of the tailpipe. I checked the cold start valve and there is fuel coming out of it when the engine is cranked. Any ideas/fixes would be much appreciated. thnx.:eek:

Mine runs at about 1000 rpms for a short while when its cold, then after 5 mins. or so it returns to 700. Does yours return to 'normal' after a while?

If you have a dud temperature sensor it might cause a high idle.

When did you last change plugs/cap/rotor?

Sounds like vac leaks and throttle linkage is off. My 560 exhibits higher idle in P than necessary.

Is the idle switch closed, is the airflow pot output below .7v? Do you have a vacuum leak.

the idle drops down to "normal" range intermittently but for the most part its 900-1000 in P and 7-800 in D. There are no vaccum leaks to be found and the cap rotor and wires have around 10,000kms on them. Just as a side note when i bought the car the cruise control had been disconnected and removed from the throttle linkages.

i replaced the cold start valve today, seemed to help the car is now idling normally in drive but still around 800-900 rpm in park. Also it does seem to intermittently idle at proper rpm sometimes. could there be a stuck valve somewhere? it really has me boggled, i think the car is possessed!!!! thinking maybe a bad temp sensor? when u guys say a dud temp sensor, do you mean the engine temp sensor or the coolant temp sensor? thanx:D