Mercedes: petrol supply system problem, mercedes benz c, mercedes benz c 180

Question
Dear whunter,

My car is a 1995 mercedes-benz c 180 model. when I drive my car and wait for a traffic light,
the engine does not run smoothly. sometimes the engine even stops. This happens quite often,at least 10 to 20 times per week. The problem comes when:
1. wait for the traffic light, or drive from an
idle status.
2.when there are more people in the car, say 3 to 4 people waiting for a traffic light and start driving from idle status.
3. when the air conditioned is on with cool air in summer (this causes the problem each time).
4. the problem is worse in summer than in winter.

But,there is not a little problem when driving in
a high speed, say 30 to 100 km/h.

I went to different authorized mercedes car
repairers. they check my car with different answers. (my car's problem comes when the engine is on with gear in driving position, they all
check my car either in engine stopping situation
or engine on but gear in parking position)

one repairer used computer to check my car and
said there was not problem found in my car; the other said I need to change entire petrol system to solve the problem. because the car itself has
a computer system controlling the feul injection.
this computer system has memory to keep past driving record. the new petrol system can change the old record and solve the problem; the third one even said the engine need to be replaced.

I had no choice and alleviate the problem by the
following ways:
1.keep petrol in full tank most of time. whenever
there is half tank of petrol, the problem comes frequantely, and whenever the petrol is full tank, the problem reduce greatly, even disappear.
2. whenever problem comes, open the petrol tank lid to change the presure in the tank.
3. press accelarator hard to the end to allow
more petrol runing to spark plug for a few second when driving, and then return to normal
speed.
4. change spark plugs

the problem can come at any time and disappear at any time in idle or low speed status. there is not a problem in a high speed status.

From the ways I do to alleviate the problem, I guess, there must be some problem with petrol
pump (too old), or petrol pipe (leaking air) or petrol filter/pipe (brock with dirt).

please advise me what is the problem and how to solve it.

Best regards

William


Answer
Best guess:
#1. Fuel system is building vacuum = bad regeneration valve in closed fuel-evaporation-control system.
#2. Bad air-mass sensor.
#3. Bad wiring.

MB Engine Wiring Harness Failure
http://www.mercedesshop.com/shopforum/showthread.php?p=927185#post927185