My car is a 1993 280TE (2.8L, 104 engine) right hand drive, auto box, with 92K on the clook and in first class condition.
However, when stopping at traffic lights or similar the engine nearly dies and then revs up. At times the idle is a bit irregular and the engine kind of vibrates a bit. Things are worse if Air Con is on. On two or three occasions the car stalled when I steered into full lock.
I understand the OVP relay could be an issue. The one in my car is part number 000 540 67 45 and seems to be the original as it has a date on it indicating Nov. 1992.
I had that on my 104 ,it was injector o-ring - It ran fine in gear over 2000 rpm.
Once stopped at a light it would swing 500 - 1200 rpm . Full lock steering loads the PS pump which could stall a low rpm idle .
i had a similar problem on my 93 300e . it turned out to be the mass air meter . about 300 bucks for the part and about 5 minutes to install .
try this ..... open your hood when the idle starts surging , unplug the mass air sensor and then plug it right back in . if the idle staightens right out then the mass air sensor is your problem . I am not really sure why this trick works , but it does ..
Thank you very much to both Uboater and Mustangman for your suggestions. I'll be working on them as soon as I can.
BTW, I forgot to mention that the car is difficult to start on cold weather. You have to crank the engine for ages and smells strongly of unburnt petrol. At times helps if I press the accelerator fully. When the engine is at operating temperature there is no problem.
I have a similar problem and it is killing me right now!!!
In traffic, at stoplights, when immobilized, the idle is at 500 rpm. Sometimes, it takes a rather unpleasant drop to 400 rpm, vibrates and even STALLS (chokes?) sometimes. And then I look like a dork slowing down traffic in my old Merc.
Anyone could help me on this please, I really don't wanna go to a garage where they will ask a crazy price for things that were not necessary...
Does this car have a fuel injection temperature sensor, also called the coolant temperature sensor ? If yes, check if this is working. On my 260E, resistance across the sensor should be 2.5-3.5K at 20 deg-C and 250-350 ohms at 80 deg-c enigne temp.
Hello to you all!
Some update. I replaced the OVP relay on sunday with a brand new Mercedes unit (£62). The idle surge is NEARLY gone but when using the A/C is at least as bad as before!
Under the car, exhaust pipe prior to the cats. An easy DYI job. Plug connections are located under the passenger side floor carpets.
It will be easy to see as it's the only thing with wires coming from it out of the exhaust pipe. There is also a removable, protective shield on the leading side of the sensor.
Idle surge 
Linear Mode
