Rougher Idle with air cleaner removed
 

I have been chasing a rough idle problem with my 1994 SL500 for almost a year now. As recommended by a few folks here, the intake manifold gasket was checked by spraying something non-flammable around the gasket. I noticed that when I removed the air cleaner assembly that the idle of the engine would vary quiet a bit anytime the wind blew. I could even stall the engine by blowing into the air flow sensor. I temporarily replaced the air flow meter and the other one did the same thing. Is this normal behavior? (The throttle body assembly had been replaced about a year ago and I'm wondering if it could be bad.) Thanks!

Somebody ( like me ;) ) ,is going to tell you, the reception on the Crystal Ball is not working very good.
Can you tell us the model & year of your car ?

Ooops... I thought it was in my signature. I updated my message. Thanks!

When a throttle body gets replaced, there are a few rubber hoses that usually get replaced (because they're usually brittle and break). It is also easy to break the plastic vacuum tubing in that area. On my E420 (also an M119), I had the fuel pressure regulator dripping a little - might want to check yours, since you're there. (it's on the U shaped Stainless steel fuel tube, near the driver - a search for the part reveals a picture to go by) After running for a minute, shut it off, pull off the tube, and wait a minute or two, if you do not notice any wetness/fuel at first. If it stays dry even after a few minutes, you can cross that item off your list of possible culprits.

The mechanic did inspect all of the vacuum hoses and didn't find a leak. I don't think I understand the role of the fuel pressure regular leaking. Do you mean that is can cause a rough idle? (The engine runs great once it's not idling.)

If the regulator leaks, fuel gets sucked into the intake manifold - it could mess up the mixture if enough gets spewed into there. The odds of this being the culprit aren't betting odds, but worth looking into, in my opinion. (can't hurt, and best of all, it's free)

Thanks for suggestion. After thinking about it further, I don't understand how that can cause a rough idle. The pressure in the fuel line should be constant and the injectors would seem to determine when the fuel enters the cylinder.

The rough idle I'm normally experiencing seems to be related to the outside air, as I only really have a problem if it's cold and damp or if the wind is blowing while standing still.

The question I had was that the engine became erratic when a breeze blew while the air cleaner was removed. I can possibly understand how it could happen, since a breeze could be causing a vacuum and drawing air from the engine. This is just theory trying to explain observed behavior. The real question is this normal behavior? (I don't remember having this kind of problem with a carb.

Is anyone able to tell me if this is normal behavior? Thanks!

my 92 500sel can stall if i air will blow hard into maf meter.

It is not quite possible for the ambient air to blow across the MAFS and stall the machine. There are also after market forced air charger that forces more air into the throttle body in a bid to increase performance.

Though I can't really explain how the breeze is causing the engine to stall, but I would say the engine will only stall if you pull the Sensor plate up. Pushing it down would rev the engine as you are giving what the engine needs : air.

Thanks and hope it helps