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I have a 1981 380SL that has a rough idle and poor acceleration for about 5 minutes just after starting when engine is cold. The car runs great after that, although infrequently it will cut out when coasting to a stop. Any ideas?
 

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Thanks

I'll look into these. I've got a CD version of the manual, which is quasi helpful. Someone told me that it could be a bad temp sensor, but there are 3 of these mounted in the front of the engine. Do you agree that these are worth examining, and if so, which one sends a signal for fuel injection?
 

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I have a 1981 380SL that has a rough idle and poor acceleration for about 5 minutes just after starting when engine is cold. The car runs great after that, although infrequently it will cut out when coasting to a stop. Any ideas?
If you would put that 1981 380SL in your profile, under the user control panel, it simplifies things for everyone. Specially us over 50's.
The accumulator can often give fuel starving symptoms as described. Used to cost a hundred, haven't priced them lately. Don't go expensive if you don't have to. Ron, at GermanStar, will do you right.
That ought to be worth some mod points, to be brokered later.
 

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Thanks to IsthisDave and Benztoy. It's good to know your out there. I'll try some of the tests listed in the link.
How do I enter a profile? I'll also give a shot at a picture (Avatar?)
 

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Thanks to IsthisDave and Benztoy. It's good to know your out there. I'll try some of the tests listed in the link.
How do I enter a profile? I'll also give a shot at a picture (Avatar?)
User CP, at the center top.
 

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1980 450 SL
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My '80 450SL had identical symptoms (other than the random cutoffs), and it was cured with a rebuilt warm-up regulator from GermanStar.

I don't know whether the random cutoffs point to a different source for both problems, or whether it's coincidental. My guess is that it's coincidental.
 

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I have the same problems, checked and replace the plugs and wires, fuel pump. ohm the warm up regulator 18ohm where it is supposed to be. I suspect either a bad fuel pressure regulator, accumulator or bad cold start valve. I read that the warming element in the warm up regulator can be good but the diaphragm bad and need cleaning. problem with that... it needs to be adjusted after opening and its a pain.
 

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Forum Administrator , RC Colas® & Moon Pies®
1981 380SL 151K: 2005 S500 116K
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Thanks to IsthisDave and Benztoy. It's good to know your out there.
Some of us, on the other hand, lock our doors and windows tightly at night for that very reason.


Meanwhile...

Let us know how it turns out McG. Good hunting.
 

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1998 SL500, 1959 220S, 1970 280SL
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If the car(s) start easily, then don't worry about the CSV or TTS, since they are only active for a second or two, and then only below 50 degrees. The warm-up regulator is a likely culprit, but it's an expensive gamble. You can buy a pressure gauge setup for about $40 and test it.

One common problem with WUR's that has an easy fix is that the inlet screen gets clogged and raises control pressure. You can unhook the large line, unscrew the fitting and fish the inlet screen out with a pick. It has four layers of mesh. Clean it with carb or throttle body spray and reinstall.
 

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1988 560SL Currently, 1972 350SL (RIP)
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My 88 560 has the same symptoms that many in this thread talk about but I don’t think my car has a warm up regulator, please correct me if I’m wrong there but if that’s true would you say I should check the cold start valve or what else could cause these symptoms in a 560?

My exact symptoms are car starts 9/10 times fine but it’s really rough and idle is low for warm up, like bouncing between 500-800 so I hold the gas around 1000-1100 until it warms up and my car drives beautifully after that. While it’s rough and idle is bouncing up and down it takes about a minute, maybe slightly less and then I hear a sudden change and boom car runs perfectly, like a switch went off.

No black smoke, no white smoke or any smoke at all, just rough and up and down idle until warmed up. I’ll search the forum for how to diagnose once smarter than myself members help pinpoint what I should check, I just haven’t found a thread yet that seemed close enough to my symptoms until this one and then after trying to search for a WUR I realized this car doesn’t have one(I think)
 

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1988 560SL Currently, 1972 350SL (RIP)
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I won’t keep bumping this but just wanted to give it another chance as I have a drive planned for next week and would love to tackle this over the weekend.

If you don’t want to read my long post above, the gist is: my car starts rough, low idle and after about 45 seconds something “clicks” (not audibly but just mean like it suddenly changes) and runs beautifully. Thought it was my WUR but after looking for one I realized I don’t have a WUR on an 88. Where else should I be looking? Cold start valve? I thought that was only a few seconds not a minute... I’m lost
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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Maybe your Cold Start Valve, which is similar to a fuel injector, is not spraying fuel properly.
OR, maybe it just needs an "Italian Tuneup" ... how often do you drive this 560SL?
 

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1981 Mercedes Benz 380SL
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I have the same problem with my 81 380SL as well. I always let it warm up for around 5 minutes otherwise the car will be extremely hesitant and can even stall out and die.
 

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1988 560SL Currently, 1972 350SL (RIP)
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I drive it almost every day, let’s say 4-5 days a week. I e done a few italian tune ups and it’s really helped normal driving after warm up but this issue persists. Just sounds exactly like this WUR issue, just wish I knew what replaces the WUR functions on a 560 unless i’m mistaken and it does have a WUR. I was thinking cold start too but I read that’s only the first few seconds not something that should affect almost a full minute. It’s not horrible so i’ll just keep warming her up nicely but if anyone has fixed this or similar sounding symptoms on a 560 I’d love to hear. Happy with guesses too.
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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I have the same problem with my 81 380SL as well. I always let it warm up for around 5 minutes otherwise the car will be extremely hesitant and can even stall out and die.
Have you checked the Timing on your 380SL?
Mine would stumble until I got it adjusted properly.
Need a Timing Light ... Harbor Freight has a decent one, not the cheaper one but instead the $30 one.
 

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1981 Mercedes Benz 380SL
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Have you checked the Timing on your 380SL?
Mine would stumble until I got it adjusted properly.
Need a Timing Light ... Harbor Freight has a decent one, not the cheaper one but instead the $30 one.
Tried a million different things including the timing. Replaced the fuel pump which went bad, replaced the idle control unit, had 3 different mechanics try to adjust the idle countless times etc. I do have a new fuel regulator that I've been wanting to replace because I hear that the fuel regulator can be one of the main fixes. One of the ex Mercedes mechanics I know told me that I need to get the fuel pressure adjusted as well. If anyone has any information on how that can get done please let me know.
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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I found this very informative:

 
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