Mechanics

ROUGH IDLE

1995 BMW 540i

Engine Performance problem
1995 BMW 540i V8 Two Wheel Drive Automatic 130000 miles

It runs well but from time to time it goes to rough idle. When it does this I unhook the MAS for a bit and then drive like 15 miles and hook it back up. When it goes into rough idle it doesn't shift the way it should. It goes up to 4500 rpm before it shifts. I have a check engine light for O2 senser. I replaced them and they came back on 2 weeks after I changed them. That was a year ago. I have changed the MAS. It use to fix with a bottle of heat, but that doesn't fix it any more. I know the O2 sensers needs changed, but will this fix this problem
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Darrington2046
February 8, 2010.




What o2 sensor codes are you getting? Those cars had alot of problems with vacuum leaks under the intake manifold, this will set fuel trim codes and o2 sensor codes due to unmetered air getting in the engine. Has it been tuned up? A bad plug/coil/injector can cause an intermittent misfire which will set the ight resulting in " limp mode" operation which wil lmake it shift wrong. Have it scanned to see if it has picked up any other misfire codes, this ill point you to the right cylinder to check

Tiny
Jack42
Feb 9, 2010.


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