92 735il rough running on Idle - BMW Forum

csf1975 · 02-05-2009, 06:54 AM

The car really runs rough when it is sitting and idling. but when reved up it smooths out
I have changed and cleaned almost everything. "all sensor's and plugs and wires" the car has the 3.5 straight 6 I'm lost

witeshark · 02-05-2009, 09:42 AM

I'd have a look at the intake boot for cracks; this was the issue for my E30.

marti5 · 02-05-2009, 10:27 AM

Could be the MAF.

csf1975 · 02-06-2009, 05:46 AM

It does seem like there is a massive vacum leak around the intake manifold. I will know more today when I tear into it.. but I did pull codes and the O2 sensor is saying it's bad

marti5 · 02-06-2009, 06:23 AM

Go with the air leak 1st, the o2 is probably picking up incorrect mixture values due to vaccum leak.

drivinfaster · 02-06-2009, 06:52 PM

do you have a vacuum guage?? if not, get one. it's fairly self explanitary. needle in the green is good. if it is bouncy, then there is a dead cylinder. WHY the cylinder is dead could be a few things, but one that comes to mind is a intake manifold gasket. a propane tank (like for camping lanterns) and a torch fitting with a rubber hose can be used (unlit) to 'sniff' along the intake where the 'miss' is. if the idle changes, you have found a leak. a can of carb cleaner could also do the trick, but can be tough to control in tight quarters.

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