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560SL
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Discussion Starter #1
Hi All - Sorry to ask yet another question but if anyone has any thoughts on this that'd be great.

About a week ago, I noticed that when my car hit around 80 it became difficult to accelerate - the acceleration became raw at that point, like I was touching a nerve. Then driving up to Vermont on Saturday it hit this point about 60MPH, even vibrating at this speed, and yesterday it seemed to actually hit the point around 40 to the point where the car was getting close to being undrivable.

I left it with a mechanic yesterday in the town I spoke to today. He doesn't know the cars, but seems knowledgeable generally. He's done some diagnosis - cap and rotor are fine, fuel pump and filter were recently changed, etc.

He thinks its the spark plugs - one appeared white to him - and that replacing them will solve the problem. Does that sound plausible? The plugs were replaced within the last year, I think. Could they foul up and cause such severe problems so soon?

(The other two issues I have that are engine-related are a vacuum leak and/or fuel supply problem that is only an issue at startup, and I have not yet checked the timing chain guides, something I've finally booked an appointment to do after finding a mechanic back home who is knowledgeable with the 107s. Could either of those two issues be related to this? The mechanic swears it can't be timing chain related which is important because I have to drive 200 miles home...)

Thanks again guys. I'll try and actually make a real contribution to the knowledge of this forum one day!
 

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US spec MB560SL 1986, Audi A4 and A6, Ford Taunus 1964 17M and 2.0 1975
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1,419 Posts
EH valve and exhaust pipe

To me your symptoms are fuel system limp home mode or blocked exhaust/catalyst.

Fuel system limp home - mode is easy diagnose by removing the EH valve 2-pole wireharness electric connector - you will notice difference if the running engine switch into limp home - mode. If not, then it is already in the limp home - mode. There can be many reasons for that.

Secondly the blocked exhaust/catalyst will stop the engine breathing at higher speed and heavier loads, I have had that once. Took a while understand what was the problem...
 

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560SL
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Discussion Starter #3
YKA - thanks for your reply...here's an update on what happened. After replacing the plugs, the car was drivable but still way rougher than before.

But I got back home and took it to a Mercedes specialist. He's going to need to do a full diagnosis of the car but took a quick look today. I asked him about the two things you flagged - exhaust problems and fuel system limp home mode. It might have been in the latter but after spark plugs were changed, it ran better; and apparently the exhaust feels OK.

He thinks it could be a vacuum leak, issues with engine or subframe mounts - there's a bunch of stuff it could be, so it needs to be carefully diagnosed. So I'll report back next week! Thanks again for advice.
 
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