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Old 03-17-2009, 04:04 PM   #1
BMWCC 4928, BMWCCA 349578
Join Date: Oct 2003
Location: London, Ontario
Posts: 621
Balanced throttle at high RPM

I've got an RMS (Vortec) S/C on an OBD1 3.2L. I'm finding that the throttle response at high RPM is problematic. For instance, if I am accellerating at FT and then back-off a little at high RPM (above 5k) the engine reacts as if I suddenly lifted completely. The car reacts strongly (even a little violently). If I increase throttle a little, I get accelleration again, but when I lift (just a little) once more, I again get the whole car pitching forwards.

I'm thinking that the blow-off valve is opening completely and dumping all the boost. Shouldn't this be gradual though? I am working with MarkD to tune the car, but I'm thinking that this is not air/fuel, but rather the blow-off valve.

What do you think? If it is blow-off valve, any recommendations on replacement?
2002 540i M Technic
1993 325is RIP
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Old 03-20-2009, 10:19 AM   #2
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Join Date: Mar 2004
Location: Ottawa
Posts: 5,847
Sounds BOV related. Is the BOV adjustable? If so, it would need to be adjusted so that it only opens at the vacuum level that is present when you are completely off-throttle.

Try just unplugging the BOV and carefully test to see if the behavior is gone. (I wouldn't run it that way for very long tho unless you like blowing up pipes. )
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Old 09-25-2009, 09:49 AM   #3
black bnr32
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Join Date: Sep 2008
Location: saskatoon
Posts: 456
Well since this was bumped anyway...

Throttle position sensor. I had a very similar scenario and that was it.
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