300SL: rough running, I'm stumped. - Mercedes-Benz Forum

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post #1 of 7 (permalink) Old 01-13-2007, 02:35 AM Thread Starter
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300SL: rough running, I'm stumped.


I'm in big trouble with my "old" car and hope I can find some help here. This may seem so crazy, you'll think I'm making it up. Here goes ...

1993 300SL. About 105k miles. Runs flawlessly, except ...
Car is no longer a daily driver. If it sits for a few days, this happens: Starts normally. Runs great for perhaps 15 minutes. Then it begins to miss, then to miss badly. After a few minutes of this it will barely keep running, to the point that it can't climb much of a hill.

After about 10 minutes of this, it starts to recover, and in another 5 minutes or so it's back to normal. After this, it stays completely normal and runs fine unless it's left to sit for a few days. Then the same behavior repeats.

Any ideas much appreciated. I'm developing a twitch here.

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post #2 of 7 (permalink) Old 01-13-2007, 06:31 AM
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Fuel filter OK?

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post #3 of 7 (permalink) Old 01-13-2007, 07:49 AM
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Condensation in the cap maybe?
Maybe time for a new cap and rotor.

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post #4 of 7 (permalink) Old 01-13-2007, 01:15 PM
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A good old-fashioned tune-up would be a great place to start, IMHO -- plugs, wires, cap, rotor, air filter, fuel filter -- and see if that helps. Assuming of course, that you haven't already done that pretty recently.

"If spending money you don't have is the height of stupidity, borrowing money to give it away is the height of insanity." -- anon
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post #5 of 7 (permalink) Old 01-13-2007, 03:38 PM Thread Starter
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Thanks to everyone who replied. I should have said that the "tune-up" level stuff should be OK. The really wierd part is the ebsolutely predictable cycle of runs good - barely runs - runs good over about a 1/2 hour period after cold start. And only if the car has had a couple of days off.

I feel as though it may be somehow related to the engine warming up, but I'm not sure how to run with that idea. The temp gauge comes up normally, and coolant level is OK.

Thanks again,
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post #6 of 7 (permalink) Old 01-13-2007, 03:58 PM
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Check the catalitic converters....As strange as it may sound my old Caddy had the same problem and is was a plugged converter.
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post #7 of 7 (permalink) Old 01-21-2008, 03:05 PM
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temp sensor

same prob on my 92 300sl 24v been told its most likely temp sensor miss reporting to cpu
need to know were it is to check it ??
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