89 300TE Stalling

[Glick]

With the A/C on, when coming to a stop or slowing quickly to make a turn, the RPMs will drop and stall, sometimes they will pick back up but never under hard braking. With the A/C off, it doesn't seem to be so much a problem, however, if I plan my stops and slow gradually, it doesn't seem to stall (A/C on or off). Appears to be more of a problem when the engine warms up. I've replaced the following items: Plug wires (helped immensley since the others were arcing and you could hearing standing next to the car with the hood open), cap, rotor, vacuum hose from idle control to the rubber part under the fuel distributor and the rubber part under the fuel distributor. There is no EGR valve on my model. Any ideas?

[David C Klasse]

Never fails, does it!?
DEFINITLY sounds like a symptom of the infamous OverVolt Protection Relay, AKA OVP. Do a search on "OVP" and you'll come up with loads of info.

On late 80's and early 90s 6 cylinder engines, the OVP was many times faulty causing stalling, no warm-engine starts (cranks, but no fire), and the ABS light illuminated. It's only a 50 dollar part and you can change it yourself! Many of the soldier joints were bad (made in Hungary?) and also jump-starting with the Mercedes can cause it to go bad.

GOOD LUCK!

[psfred]

Did you replace both hoses (from the fuel distributor to the idle control valve, and from idle control valve to manifold)? Mine were rock hard and loose on the nipples, causing serious air leaks. This can cause stalling.

Check all the other vacuum line rubber connectors, especially the line to the control unit on the fender -- leaks here can screw up the mixture control, causing either over rich or over lean idle. Most of the rubber bits are shot by now. I replaced all of them -- cured hard shift problems at the same time.

Also, did you clean the idle control valve -- you can just take it off and spray in some carb cleaner, shake with a thumb or some such over the holes, then dump the carb cleaner, repeating until no more crud or color comes out. The idle valve, when dirty, will stick closed, causing the car to stall. Can also cause rough idle as it jerks rather than moves smoothly to control idle speed. I've not cleaned mine, but will soon, as Mom is complaining about stalling with the AC on.

If this doesn't fix it, get the idle mixture checked -- if it was set with leaking hoses, it is now too rich.

If that is OK, then the OVP relay is a likely culprit -- causes stalling by killing the voltage to the mixture control circuit.

Peter