how do i stop my 1991 M\B 300SEL from stalling at a light?the rpm's come down and keep going...no warning

Answer 1

Search for an idle air control in an on-line parts store. Remember its mugshot. Remove the air cleaner. The largest rubber tube exiting the air-flow plate housing (will be on the end opposite the fuel distributor) will lead to the IAC. Do not be timid. Although its M-B and part of some complicated-looking plumbing, the thingy is no big deal, you won't mess up unless you are extraordinarily reckless. Take some digital pics, just to feel more safe.

Pull the IAC and use starting fluid or carb cleaner to flush it. If you can get cotton swabs in there and see what you are doing, go for it. Removal of this gunk will correct the problem where it is occurring intermittently.

You should be able to get the part out with screwdrivers for the air hose clamps and the carb cleaner or start-fluid.

If this doesn't cure it, chances are the idle control unit is dead.
Can also be a dead valve, but most likely, in order, 1) gunky valve, 2) dead control unit, 3) dead valve, 4) bad wires.

A competent shop should take less than one hour to sort it out and change whatever part, unless its in the wiring.

Answer 2

I also have a W126 though it's a V8. The problem may be your idle speed control, possibly the attached valve. I don't know where it is on the 300. In some cases the control merely needs to have electrical contacts cleaned, in others resoldering internal circuits is all that is needed (if I recall correctly). I suggest you log on to one of the excellent MB discussion groups, there are still keen W126 owners about.

Answer 3

Check the idle control valve. Also does it happen more when the a/c is on? If so check and see if the sensor that turns up the idle is working. Also check the air boots for cracks. Small leaks in them can often cause these kind of problems.