m119 hard starting when cold, erratic idle
 

92 500SL, 102k miles, 2 owner car, same owner past 14 years with full records. All the typical issues have been addressed over the years, and it just had a 30k major about 1k ago (before I bought it). Car runs out great, starts right up when warm, but when it's been sitting long enough to be fully cooled off, it is slow to turn, then gets a high-pitch turn, briefly, then slows back down. I let off, crank again, and voila - cranks right up. When it's already been running, starts right up as well.

Also, whenever I put it in park after driving, the idle goes a few hundred RPM too high.

On my 400E, starting is very robust, roars to life. The SL sort of slowly rises to life. Battery good. My seat of the pants sensation is a fuel delivery issue.

Ideas?

Have you looked closely at the distributor caps & rotors for moisture?

When the idle goes high, does the ASR lamp come on?

I havent checked the caps. It has been quite wet lately, so could explain it. I'll take a look.

No ASR, however I do get a very occasional SRS lamp that quickly goes away, from time to time

ASR should have been standard on a 92 500SL.

Right, I meant I have no ASR MIL illuminated. :)

Ok, found in the extensive list of records caps replaced at 71k, 2003, then "cleaned" at 98k, or 9 months ago.

Same likely culprit?

Cleaning green from the dist cap is a band aid repair, to sell a car!

My sentiments exactly........I'd never heard of this before. lol. I'll replace them :)

Caps/rotors replaced, no change. Sigh. They were black and green, with some hairline cracks, so probably not a bad move, just not totally necessary (yet). My gut feeling is still fuel pressure....hard to describe, but a clear difference from my 400e, which roars to life. This one trickles to life. It's kind of like the sensation of a weak pee stream. Not that I would know. I'm not kidding!

A 4-5 second cranking time is "normal" for a CIS-E system engine.

Fuel pressure bleed-off would have a greater effect on a hot-soak re-start than cold start.

Coolant temp sensor signal is the MOST important signal for cold starts.

And I replaced one on the 400E, forgot what for - I think it was fuel economy issues. I'll pick one up and try, cheap possibility. Thanks

I recently replaced the lower wiring harness on my coupe, and while I had everything apart I noticed the starter looked original. Since on a few occasions over the course of a year I had gotten a "click" on a very hot start, and the car was 16 years/130K old, I decided to change the starter as well. I was very pleased to find a much faster cranking speed which has completely gotten rid of the long crank/2nd try start that was sometimes very irritating. I've always thought that either a starter turns or doesn't, but never considered that an old starter might turn slowly enough to cause hard starting problems.