1988 Mercedes, 260E, inline 6 cyl. Engine: 103.

Symptoms: The car will start and idle fine (at about 1,000 RPMs) until I drive it for 15 minutes. After that time, the car will start to hesitate, but only during acceleration and when it is idling. At first the problem is only notable at lower RMPs of acceleration (500 - 2,500 RMPs). As the car is driven longer, the hesitation migrates into the whole spectrum of RPMs during acceleration. Before the hesitation occurs, the car seems to have poor acceleration and very little torque, especially at lower RPMs. I have a hard time getting it to spin in the snow . Also notable, the symptoms do not seem to be a function of the engine's temperature, the engine always reaches a running temp of (~80 C) 5 to 10 minutes before the problem is apparent.

Work done:
Replaced the Spark Plugs (significantly helped, info below...)
Replaced the Distributor Cap and Rotor (no change in performance)

Background Information: I recently drove the car on a 1,500 mile trip. About 1,000 miles through the trip it started to hesitate during acceleration. When I arrived, I noticed that it was hard to start and it ran poorly. I replaced the spark plugs. Afterwards it started easily but, I noticed the problem would reoccur after ~15 minutes on the road. So, I replaced the distributor cap that was in poor condition, picture below. This did not make the symptoms change much, and if anything, made it a little worse.

Any ideas would be greatly appreciated because I am 1,500 mile from home...

::Kyle

Disclaimer: My car is a 1988 560SL but I believe the fuel injection system is the same.

I had identical symptoms when I first aquired my car. I believe you have more than one fault. The high idle is probably a vacuum leak. If your car has an "ECONOMY" gauge (actually just a vacuum gauge) it must be pegged to the left when idling. If it is not you have a vacuum leak that will affect your idle among other things.

The driveability issue worsens when the engine warms thus indicating a temperature problem. In my case the culprit was the engine temperature sensor that inputs to the fuel injection computer. An easy DIY fix by replacing a reasonably priced and accessible component. I don't know where yours is located but you will find it screwed into the intake manifold somewhere. It should have two wires connected to the top.

Good luck and let us know what you find out regardless of the outcome.

There may be a lot of reasons.

Have a look to the moulded connector on the coolant temperature sensor ( double sensor on the clutch side, on the head) the wire is red green. It may be damaged (can be obtained as a spare ref 013 545 87 28).


have a look also to the thermovalve on the head

Do not change part without having found the real cause it will lead to waste of money.

good luck

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Keep us posted especially if your problem is solved
Present cars:
My car: E-class 420CDI, 2008, W211, V8, 180 000km

Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km

Son's one: GLK class 220CDI, 2009, W204

Sold E class 260E, W124, 1988 beloved car sold after 489 000 kilometres of reliable services (engine M103, clutch and 5 speed manual gear box all original).

E-class, W210 320CDI, 2000[/B], 225 000km, Sold

Thanks for the suggestions.

I still do not believe that the problem is a direct function of engine temperature. The temperature gauge will show a hot engine long before the problem is apparent.

Also, the lack of torque is becoming much more noticeable ALL the time.

I did not mean to imply a possible overheating problem. The temp sensor I mentioned comes into play when the engine reaches normal operating temperature, say after about 15 minutes of driving.