I have a 1993 E280

I've noticed over the recent months, the rpm fluctuates from 300 to 1200 while idling especially when I have just driven for a short distance after a cold start. The Mercedes agent have hooked up a laptop computer diagnostic to check the problem but found nothing.

Just 2 days ago I notice that from a standstill at the traffic light, if I step hard on the accelerator to drive off, the car seems to stall, hesitate for while, and then move off. Another mechanic checked the fuel pump and found nothing either.

Then the car really started stalling, especially if I start the car from stand still. I almost had to tow the car back. But after revving the engine gentling (to prevent stalling) for a while, and driving slowly for a while the problem seems to resolve.

What is the problem ? Can a faulty alternator cause this ?

Wow, That’s a lot of things going wrong all at once. I will start with the fluctuations in idle. It sounds like the HFM meter is giving some faults, or the fuel mixture is at one of the limits. The stalling might be caused by a faulty over-voltage protection relay. Some of these things could be an intermittant failure and not show up as a fault on the magic computer. Sometimes the technicians need to use that thing between their ears and listen to the customer complaints instead of relying on a machine to give them the magical cure. A side note: Take the car into the repair shop when the thing is acting up!

TAKE A LOOK BENZMAC SUBJECT " CHECK YOUR
ENGINE WIRING HARNESS". YOUR CAR HAS THE POSSIBILITY OF A BAD ENGINE WIRING HARNESS!

I had the same problem in my 190E and took me six months before I found a non-MB dealer mechanic to fix it. He told me that it could be either "idle speed valve" is bad or something else. That something else turned out to be the 1/2 inch upper idle speed valve hose that was cracked and leaking vacuum. This caused my engine to go from 500-1500 rpm back and forth and stalled. When in traffic I had to keep my foot on the accelerator and one foot on the brake to keep the engine from stalling.