I have a 1988 300e with 145000 km on the engine. At idle, there is a rhythmic surge in the engine. About every second, the RPMs increase about 50 rpm and the oil gauge fluctuates between 1 and 1.25. Sometimes the car vibrates. I have had the plugs, wires, rotor and cap changed as well as the air flow meter. The head gasket has been changed as have the valve seals.

Is this normal?

The car has intermittent hesitation problems (very little power for about 5 seconds) when starting off, especially when cold ( about 1 in 10 times). It seems to be a bit worse in wetter weather. The hesitation gets better as the car warms up and most of the time disappears. I can get rid of the problem most times by tapping the accelerator a few times. Whenever a floor it, the car responds almost immediately.

There is never a problem starting but sometimes (1 in 10), the RPMs drop to 100 and the car almost but never stalls.

Could this be an OVP problem? (The fuse is working)

I've had my car to the mechanic twice in the last month for this and the car refused to show the symptoms both times- using both hot and cold starts.

Any suggestions?