Do auto trannys ever stall a motor? (ML320)
 

I still can't solve the stalling problem with this '98 ML320. It stalls when put in gear, but only when cold. It feels to me like the tranny is dragging the motor down to much when it engages. Any ideas? What could make a 75K mile tranny tight? Computer problem with converter clutch maybe?
It runs, revs, and idles fine when cold, but just can't take it when the tranny engages.
It's not the MAF, and there have never been any error codes.

Only way I could think of it being the tranny's fault is the torque converter clutch being locked when it is put in gear with the vehicle stopped. More than likely, though, I would think of the problem being on the engine side.

Short Answer - NO!
 

An automatic transmission will not stall an engine, unless the torque converter locks when is should not.

An idle speed control actuator that does not act fast enough to keep up with the rpm drop when cold, or a sensor that does not sense engine rpm properly, will allow rpm to drop until the engine stalls.

The engine computer senses idle speed, and controls it to keep a constant rpm. The transmission is just another variable load, like the A/C compressor, power steering pump, and alternator as far as idle rpm.

I don't know the specifics of how the idle speed is controlled on this engine, but your technician can check it.

Best Regards,

Jim

Idle speed is controlled by the engine computer and electronic throttle actuator. There is not seperate idle circuit and idle control valve. More than likely there is a control problem with the engine.

Any clunking going on? Notice any ruffer ride? I wonder if the tranny/motor mounts are bad messing with the alignment of things that engage.
But you say only when cold?
Maybe a vacuum thing...?
I give up.
Good luck.

My 190E would occasionally stall when engaging Drive when the engine is cold as it loads the engine somewhat, and my car was missing and sort of cold-start high idle so was rather 'stumbley' and asking to stall until warmed up!.


Russ

The symptom of a torque converter stall at a dead stop in gear, is an immediate abrupt stopping, stalling of the engine, if the engine lugs and chugs for a while it’s an engine control problem.

Thanks for the replies!
If it is the engine control, would the load of the tranny be great enough to kill the motor? Seems kind of hard to believe, but the converter is very low stall.
I am able to keep the motor alive by flooring it for a second just before the tranny engages, not 1/2 throttle, not 3/4, but 100% does the trick. A half second after engagement I let off the gas and all is well. I can even switch back to neutral and drive normally after this. Unfortunately, this is my 60yr old mothers car and she won't even attempt to try that. I assume that flooring it pulls the computer out of it's closed-loop mode and is the only reason I can get the fuel I need for that second? If fuel or the computer is the problem, then why does it not stall after I force it to stay alive? That's where I'm thinking tranny....

There are no other problems, no noise, mileage and power are fine etc.
As I predicted, the local MB dealer claimed it was the MAF, but it is not. I still had to pay their $50 diagnostic fee. :mad:
The dealer said they have no clue what's wrong and I'm on my own. :confused: