w126 500se rough idle and stalling when hot

starwars

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new to the forum so please feel free to correct any breaches of etiquette around my post

I am a bit stumped by this. When hot and in drive the engine sometimes develops a very rough idle and will stall, and is usually a bit tricky to restart. Occasionally difficult to start in very hot weather as well. The rest of the time the idle is a bit rough but at the correct RPM and there is a smell of unburnt fuel. It usually takes a second or two to settle at the correct cold starting RPM. When under load there is no problem at all with power delivery and it is consistently 23-25mpg. No sign of any vacuum leaks. Newish fuel pumps, plugs, coil, etc. Car is in exceptional condition and <100k miles.

Irritating intermittent issue that undermines confidence as I do around 5,000 miles a year in it. Absolutely love it and my teenagers all prefer being driven in this car rather than a modern car.

Love to hear any ideas.

Thanks
 

Blobcat

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Hello and welcome

Think it might be your engine that can suffer from condensation in the distributor cap. Plenty of posts on the forum about it. Give it a clean and a bit of Vaseline
 
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starwars

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Thanks very much Blobcat. Looking at the other posts that certainly sounds like it. Must have used the wrong search terms previously. Good to see the combination with a 110, shows good taste in cars, I have 2x td5s as well. Will report back if that fixes it but it is intermittent so might take a while to be sure.
 

Blobcat

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Thanks very much Blobcat. Looking at the other posts that certainly sounds like it. Must have used the wrong search terms previously. Good to see the combination with a 110, shows good taste in cars, I have 2x td5s as well. Will report back if that fixes it but it is intermittent so might take a while to be sure.
TD5 is nice just don't get them wet... 200tdi is "almost" unbreakable... :rolleyes:
 
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starwars

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Thanks again so far so good and cleaning the rotor seems to have improved the idling as well although still not perfect.

But one TD5 has a tuning package on it and now gets close to 200bhp - makes a huge difference.
 

Blobcat

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Thanks again so far so good and cleaning the rotor seems to have improved the idling as well although still not perfect.

But one TD5 has a tuning package on it and now gets close to 200bhp - makes a huge difference.
My 200TDI will do 90mph... should I want to... it has a somewhat modified engine :cool:
Rest of it is much happier at 50-60 though, or below 10 when I’m seriously off-road...:p
 

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