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BMWDoc
BMWDoc, Independent BMW shop owner
Category: BMW
Satisfied Customers: 6456
Experience:  20 years of experience working with BMW's. Independent European shop owner and technician.
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2000 bmw 740i: running lean..cause and repair procedure, thank you

Customer Question

2000 bmw 740i, has a 1634 code, running lean, bank 1 and 2. would like to find out cause and repair procedure, thank you
Submitted: 5 years ago.
Category: BMW
Expert:  BMWDoc replied 5 years ago.

BMWDoc :

Hello, I'm Jason. I will do my best to answer your question quickly and accurately using the information you have provided.

BMWDoc :

hello there. How many miles are on the car?

JACUSTOMER-ulukvei0- :

hello, 135000

BMWDoc :

while I'm waiting, you're going to need to check for vacuum leaks using an inert smoke generator. Also, if you're starting to see any oil smoke on cold starts, it's very likely that you will need to start by replacing the air/oil separator on the rear of the intake manifold

BMWDoc :

this is the typical cause of lean running codes....

BMWDoc :

and if, while the car is idling, and you try to remove the oil cap, and you experience a lot of vacuum, this is another sign of a failed separator valve

BMWDoc :

if you do need to replace the valve, it's best to remove the whole intake, as the torx bolts holding the separator on will typically strip if you attempt to remove them with the intake in place

JACUSTOMER-ulukvei0- :

and that is located on the rear of the intake/

JACUSTOMER-ulukvei0- :

?

BMWDoc :

correct. This picture is from a '98, but very similar

Full Size Image

BMWDoc :

Another view:

Full Size Image

BMWDoc :

And finally, what it looks like off the intake

Full Size Image

BMWDoc :

If this is the problem, I also recommend a few set of intake gaskets, the front intake cover gasket, the tube that goes through the center of the intake, and the vent tube that runs just to the inside of the left cylinder bank, in the valley

JACUSTOMER-ulukvei0- :

will this also cause no thottle response with accerator pedal?

JACUSTOMER-ulukvei0- :

will this also cause no throttle response with accerator pedal?

BMWDoc :

that would have been helpful information in your initial question. Possible, but not likely

BMWDoc :

you could also have a failing air mass meter

JACUSTOMER-ulukvei0- :

well i do have vacum when oil cap is removed, step on gas pedal while running, will not revive up, backfires at idle, will not accelerate

BMWDoc :

could be multiple problems, but the two I've indicated are the most common. Any diagnosis beyond that is somewhat beyond the scope of this format