Help!!!!!!!!!!!!!!!
- Thread starter Kenny2g
- Start date
Probably not the oxygen sensor.
Could be a vacuum leak. Does it idle rough? Does it want to shut off at any engine RPM, or mostly just at idle?
The master brake cylinder is vacuum assisted. When you press the pedal, engine vacuum is used to actuate the master cylinder. If vacuum is already low, pressing the pedal needs more vaccum and the engine stutters. I have seen this, but it wasn't a bimmer.
Could be a vacuum leak. Does it idle rough? Does it want to shut off at any engine RPM, or mostly just at idle?
The master brake cylinder is vacuum assisted. When you press the pedal, engine vacuum is used to actuate the master cylinder. If vacuum is already low, pressing the pedal needs more vaccum and the engine stutters. I have seen this, but it wasn't a bimmer.
XLibelle's suggestion is a good place to start. You need to try to find a vacuum leak, so you need to locate all the vacuum hoses, check for cracks, broken lines, etc. This can be a real challenge, that's why the spray can help.
Vacuum lines are used typically in the following systems: Brake master cylinder booster, emissions controls, heating/cooling (under dash to move air divert vanes for upper/lower vents, etc.), iginition timing (on older vacuum advance distributors, yours is probably electronic?). My comments come from working on other brands of cars, not bimmer specific, I assume bimmers are similar.
Look for cracks, dry rotting due to heat, etc. Look for vacuum lines that have rubbed against something over the years to the point of wearing thru to the center. I had this on my Volvo with a hard plastic vacuum line. The easy fix is to cut the bad section out and splice it with rubber vacuum hose.
The brake booster has a rubber diaphragm inside. If the diaphragm cracks, air leaks in. The interesting part is that it can crack such that it's sealed when the pedal is not pressed, but when you step on it, the crack opens up and air gets through. This is EXACTLY what happend after only 6 YEARS (GM crap!) on my '95 Suburban. It was about $125 for a new booster, I did the work myself, probably about 2-3 hours labor at a shop. The clue was that I could HEAR the leak when I pressed the pedal. I heard it for about a month, it got louder and the brake assist was getting noticeably weaker.
Obviously you have to do this with the engine running. BE CAREFUL since you will be poking around lots of moving and hot parts!!!!!
Vacuum lines are used typically in the following systems: Brake master cylinder booster, emissions controls, heating/cooling (under dash to move air divert vanes for upper/lower vents, etc.), iginition timing (on older vacuum advance distributors, yours is probably electronic?). My comments come from working on other brands of cars, not bimmer specific, I assume bimmers are similar.
Look for cracks, dry rotting due to heat, etc. Look for vacuum lines that have rubbed against something over the years to the point of wearing thru to the center. I had this on my Volvo with a hard plastic vacuum line. The easy fix is to cut the bad section out and splice it with rubber vacuum hose.
The brake booster has a rubber diaphragm inside. If the diaphragm cracks, air leaks in. The interesting part is that it can crack such that it's sealed when the pedal is not pressed, but when you step on it, the crack opens up and air gets through. This is EXACTLY what happend after only 6 YEARS (GM crap!) on my '95 Suburban. It was about $125 for a new booster, I did the work myself, probably about 2-3 hours labor at a shop. The clue was that I could HEAR the leak when I pressed the pedal. I heard it for about a month, it got louder and the brake assist was getting noticeably weaker.
Obviously you have to do this with the engine running. BE CAREFUL since you will be poking around lots of moving and hot parts!!!!!