E280 Erratic Idle Problem

Hi

I have a 1996 UK supplied standard configuration Mercedes E280 which I have recently bought via an approved Merc dealer. The car has 26000 miles on the clock (verified) and has full Mercedes service history. It has the standard 4 speed auto box with Sport and Normal settings.

The problem is that my wife (who uses the car daily) does a lot of city driving and has found that the idle speed when the car is stationary in traffic (in Drive) intermittently goes from about 600 to 1000 rpm and back again repeatedly. This makes the car very unpredicatable to drive. It is even worse in reverse!

The car has been back to the local Merc dealer about 4 times now and they have put it on their computer and found no fault and also done a manual check and a 50 mile roadtest. They have replaced the lamda probe but this has not cured the problem, Fortunately the car is under an extended Merc warranty but it's a real pain having to let the garage have it for days on end when they seem to be getting nowhere.

Is anyone aware of this problem being documented or perhaps you've come across it before. Either way perhaps you would be kind enough to give me your thoughts so I can suggest then to the local dealer for investigation.

Note:

I've seen the now closed thread at Erratic Idle and Engine Stalling but this was asking about a similar problem to mine on a 1993 Mercedes.

Many thanks

Rob

[mbdoc]

Fuel mixture / air mass sensor can cause this type of problem, and can be hard to find. If there was any electronic accelerator/ idle speed control problem there should be a CODE in the ISC/CC computer. If air mass sensor is the problem the shop should be able to go into actual values in the HFM(fuel system) computer & read the adaptation values to see if the system is running LEAN.
Good Luck

Thanks MB DOC

regards

Rob