'92 400SE
Today we reached warm 70 oF weather and the following began to happen:

When idling, I rev up the engine, then release the throtle, and all of a sudden the engine will drop below 600RPM and die OR come very close to stalling while it hesitates to stays alive.

When I had it in REVERSE, I pressed the gas far enough to make it go above 2000RPM, the vehicle moved a fair distance and died as the RPM's were dropping. I waited a minute, and with the help of having the throttle pressed it came back to life.

While in DRIVE, I have no problems.

Recent services (500 miles):
New sparks.
New fuel filter.
New breather hose from brake booster.
Oil Change w/ ELF 5W40 LDX.

Could this be signs of a vacuum leak...or a 100 other things.

Ideas?
Thanks.

Rev to 1000RPM, then release: Engine will drop slightly below 600RPM, stay alive, without hesitation. Then rises back upto 6000RPM.

Rev to 1500RPM, then release: Engine will drop to 100-200RPM, hesistate, but stay alive. Then rises back upto 6000RPM.

Rev to 2000RPM or more, then release: Engine will hesistate, and die.

After dying, only with the gas pressed will it start again...

Anyone seen this problem, or experienced it before?
Like I mentioned, it starts and drives fine.

Thanks.

Check out the Electronic Throttle Actuators on your car- I had the same thing happen on my 300SE (W140/ 1992). As well, it wouldnt hurt to check out the Air Mass Meter as well..... However, i am more likely leaning towards the ETA as it will do what you describe when the insulation starts to fail internally and creates shorts.....

How do you go about checking it?

Just another note: I removed the airfilter housing (holds 2 engine filters) off the MAF and Revved it past 2000RPM, then it would hesitate as it droped back below 600 RPM, but would NEVER completly die. I have 2 new K&N airfilters.

Thanks.

I am not sure where the throttle is on a 400SE, but follow your throttle linkage- (The wire from the gas pedal to the trottle). Once there, you will see a metal arm that is attatched to the linkage. With the car running, if you move the arm and the throttle doesnt respond, or responds irratically- then it is the throttle assembly. ETA's (ELECTRONIC THROTTLE ASSEMBLYies) are big $$$$ at the dealer, but check out ebay and they can be 1/2 the cost. As well, do a search on ETA rebuilds, and you will see you can send it out to be rebuilt. Your car does not have a mechanical throttle. It acts as a dimmer switch- the cable pulls back on the linkage, thus sending a larger current to open the throttle wider and wider.... I learned all of this from experience!

I found the ETA to be under the MAF, in the centre of the intake manifold. I found the wire from the gas pedal, which controls the linkage that opens and closes the steel flat inside the trottle assembly.

Does the ETA control the idle? From the looks of it, while the engine is idling, the flap is competly closed...and the only way I see it being opened is by pressing the gas. It apears to respond fine while revving, just as the RPM's begin dropping, the stalling occurs. (Lack of air possibly?)

Is there a way to check fault codes, to confirm the failed / failing unit? I don't wana spend big $$$ and find it to be the MAF. I found www.4mercedes.com to be well spoken of, so I'll use them if it comes to rebuilding the unit.

Thanks again.

I don't know if your unit has the same type of system as our 420sel,but I found that when it starts to search for idle,the pot is bad,this is what gives the engine its Que to idle,and must reach a certain voltage to go into the idle faze.JNT