'86 420SEL Rough initial idle when Hot
 

Hi, my '86 has developed a different kind of rough idle problem. When starting cold, it starts instantly and idles perfectly. On a hot restart after driving, it will start quickly but shake for about 5 to 5 seconbds, then smooth out and no more problem.
It has 162000 miles, and I have owned it since December 2003 with few problems. I changed the timing chain several years ago; new plugs, injectors and seals; typical periodic maintenance such as oil changes, coolant, et al. What do you think?

Randy, my 300 did just that for 15 years, and I tried everything.
The exact symptom: when hot, the engine would fire right off, than chug-chug on what felt like 3-4 cylinders for about 5 seconds. Then one cylinder would cut in, then another, and she smoothed right out.

New injectors (2-3 sets over 10 years) seemed to help some for awhile, but not completely and not for long.
Awhile back I tried another injector set, and it totally healed it.
I think aftermarket Bosch injectors may be hit/miss; I don't know if paying 5x the price at the dealer nets any better quality. But that was certainly the root of my problem.

DG

That can be caused by the fuel pressure accumulator back by the fuel pumps going bad and leaking down when the system is hot, causing temporary lower pressure/poor engine running.

Good points; thanks. After 26 years of faithful service, anything is possible.
I replaced the original injectors with OEM circa 2004, as I was bringing her maintenance up to scratch just after purchase from the original owner. I could not tell any difference in operation then, it was good before and after. I had no reason to suspect injectors (and seals) other than the age of the car. I also replaced both fuel pumps and the filter. I was thinking somethign with the fuel distributor, maybe, as I have never done anythign to it, and I understand rotten o-rings are a major suspect there, but I don't know what the symptoms of a faulty fuel distributor are. Also, I have never done the rubber seals in the manifold.