My 1994 Mercedes s320 W140 has an irregular idling rev. when I slow down or stop on traffic lights, sometimes the the engine goes off. Many times the sound of the engine flactuates from high to low t

This sounds like a throttle control sensor

Any codes ? Surging idle or erratic just a lil more info ?

You might have to check the operation and condition of your idle control valve. These become clogged over time or wear out which causes uneven idle and stalling when operating under low revs.

Water in fuel, air filter clogged, fuel filter clogged, exhaust system restrictions

obviously your local mercedes dealer doesnt employ proper skilled mechanics or they would be able to resolve this issue for you and iam not telling you so you can tell them whats wrong as it is up to the management to employ qualified people and not 18 yr old lads and pay them a pittance for the privilage of working on a merc .

i would start by checking the idle air control valve. it may be called something else on a merc but basically it its a solenoid that controls the amount of air entering the throttlebody when at idle they tend to get sticky and slow when they are on there way out. hope that helps, i dont know if it is the answer but it is certainly worth looking at. let me know how you go

I had the same problem with the same car year and make.. it ended up being a "rev sensor" something like that or an "idle" sensor".

I've had this problem. It's most likely a large fail in one, or series of small problems in all, of these:
IAC (Idle Air Control) Valve - Will cause erratic idle
ERG (Exhaust Gas Return) Valve - Will cause irregular acceleration
*TPS (Throttle Position Sensor) - Most likely the culprit. It was my major problem. It'll cause exactly what you described.

And if you did not know this, your car is equipped with an OBD (On Board Diagnostic) system. Next time the service light comes on, whether the car is running or not, push [OFF] and [TEMP UP] on your climate control and hold for about 3 seconds. All the dash lights will come on and any error codes will be displayed where your odometer is.
Other controls are:
[FAN UP] -OK
[FAN DOWN] - Next
[OFF] - Rescan
[BI LEV] - Quit

put a can of STP oil additive into the engine if this doesnt work put another one in,if still no joy try changing the oil pump.if you dont want to change the oil pump then put 3 cans of STP in engine and sell it quick