blauer Auspuffnebel, unruhiger Leerlauf, Benzingeruch...

[Erich]

am Auspuff, Alarm in der CC (Lambdasonde), Fehlzuendungen?
Bei solchen Symptomen bitte weiterlesen. Kopiert aus einem Beitrag aus roadfly, in disem Fall war es ein 740 aus 1992:

Symptoms:
Rough idle, misfire at idle, blue smoke from exhaust, raw fuel smell from exhaust, check engine light (O2 sensor code).

Problem:
Defective "Cover plate with non-return valve". This is BMW's version of the PCV valve.

Positive diagnosis:

1) Start the engine.
2) Rev the engine a few times.
3) After revving, let the engine idle for about 10 seconds.
4) Remove oil cap.

At this point, upon removal of the oil cap, is a "suction" sound is heard as the cap is removed, or the cap required excessive effort to pull off (both of these are an indication of low crankcase pressure, or rather, excessive crankcase vacuum) then the cover plate valve is defective.

Another method: With the engine idling and the oil cap removed, place your hand (not the palm, but closed fingers) over the oil cap opening. BE VERY CAREFUL, DO NOT ALLOW YOUR FINGERS (or any other part of your body) TO ENTER THE VALVE COVER. THE TIMING CHAIN IS RIGHT THERE, AND THE TIMING CHAIN WILL REMOVE YOUR FINGERS FROM YOUR HAND WITH VERY LITTLE EFFORT. If the vacuum in the crankcase is strong enough to draw air through your fingers, then the cover plate valve is defective.

Yet another method: Remove the cover plate (see below) and then disassemble the valve. To disassemble the valve, pop the round cover off of the plate by prying up on the cover to free the cover from the tabs in the plate. Once the cover is off, the valve is exposed. The "valve" is a round disk that is held into a seat with a spring. If the disk is broken, the valve is defective.

Cover plate changing instructions:

This is best done on a cold engine, since your hand will be in contact with the engine quite a bit.

1) Remove the top engine cover.

2) Unbolt the coolant reservoir. There is no need to disconnect any of the hoses that attach to
the reservoir, just remove the (2) mounting bolts and the electrical connection to the level sensor. Once unbolted, just set the reservoir to the side.

3) Remove the insulation at the rear of the engine, between the intake manifold and the firewall. The cover plate is at the far rear (towards the back of the car) of the intake manifold, and has at least one vacuum line connecting to it (for the fuel pressure regulator). Remove the insulation piece by pulling it out from the driver's side.

4) Disconnect the "breather pipe" from the cover plate. This pipe runs parallel with the fuel rail, underneath the intake manifold, on the driver's side. To disconnect, remove the clip that holds the pipe to the cover plate. Just pull the clip up or pry the clip off with a small screwdriver. Then, with the clip removed, disconnect from the cover plate by prying the pipe away from the cover plate. The pipe will slide towards the front of the car and completely disconnect from the cover plate.

5) Disconnect any vacuum lines from the cover plate.

6) Remove the 7 bolts (Torx, maybe T25) holding the cover plate to the intake manifold.

7) Gently tap the cover plate and it will fall off.

Installation is the reverse of the removal, but note the following:

The new cover plate may have an additional vacuum port. If so, just grab a 3/8" vacuum plug from any auto parts store and plug the additional port.

Make sure the o-ring in the intake manifold that seals the cover plate to the intake is not damaged. If it is damaged, replace it.

Before re-installing the new cover plate, clean the inside of the breather tube with a rag. Once clean, coat the inside of the tube with grease. Also, coat the o-ring on the cover plate where the tube attaches with grease. This ensures that the breather tube will slide easily onto the cover plate with no fuss.