What are the symptoms of a failing MAS on a 94 R129? Is this a common fault?

 

slight backfire from air cleaner area during acceleration. sluggish acceleration.

 

Thanks Al. Apart from these symptoms, is it possible to have a rough or erratic idle and slight hesitation on acceleration? If the MAS fails completely, will it stall the engine and leave me on the side of the road?

 

if it's really bad, erratic idle is possible.

by disconnecting it, the idle will be regular but no power. the engine will run on a fixed ratio.

it won't stall on the roadside. it will go to "limp home mode". if your engine control unit is okay, it will get the value from the throttle position potentiometer.

 

Would a bad MAS also cause the car not to start when it is hot? my 95 sl500 starts great when cold, but after only 10 minutes it has a hard time accelerating from a stop and will stall. Also, if it cuts off, it will not start. I have to wait an hour or more for it to cool down until it will turn over again. Obviously this is a big problem in the summer because the car get hotter and stays hot longer.

 

yours is crankshaft position sensor problem.

car can still start even if the airmass sensor is faulty. there is substitute value for it to keep the engine in limp home mode. but engine will run rough and with very limited acceleration.