420SEL High tickover when warm
 

Just one more question!

When cold, the car idles in park or neutral at about 750-850rpm, and engagement into drive or reverse is smooth.

When the car reaches operating temperature, it idles in park or neutral at 1500rpm, and engagement into drive or reverse creates a big 'clunk', and once drive or reverse is engaged, it drops back down to about 750-850rpm.

I'm getting the valve seals, guides and the head done over the next month or so. Will this solve the problem, or is it an idling problem?

Thanks again everyone

When you put your gear selector into drive or reverse and you hear or feel a big clunk, it's probably work out rubber flex discs on your driveshaft, or possible a worn out center support bearing on the driveshaft.

It could also be broken differential mounts, but my money is on worn out flex discs.

You need to get this looked at right away. If it's a worn out flex disc, and it fails when your on the road, you could be looking at some expensive damage.

Other than the clunking when tranny put in gear - my 560sel (1988) has just started the same thing. Idle is smooth and about 850RPM when cold and after about 15 minutes it starts to climb to 1500RPM at idle and stays there. However, when I put it in gear, when warm and idling at 1500RPM, it smoothly goes down to 650RPM. When I take it out of gear when warm, it takes about 3-5 seconds and slowly goes back to 1500RPM. Other than that the car runs good. Any one with ideas????:confused: :confused: :confused:

Its probably the idle control valve. It has been discussed to death in many threads. Do a search.