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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > RPMs dipping under constant speed



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      09-01-2012, 10:08 AM   #1
tmurphy2
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I swear one day my car will actually work. Under constant speed say traveling at 70 mph on the highway, the car will pull back and almost feel like its running out of gas or something. If 70 mph puts my at 2000 the car will go 1800 then back to 2000.... 1800 then back to 2000. It gets more severe while traveling downhill. It's fine under all types of acceleration. Fuel pump?
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      09-01-2012, 05:57 PM   #2
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bump for some help.
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e92 335i sport[/b] 2 GO: Cobb AP Stg 2+, Macht Schnell DPs, Injen intake, Spearco FMIC, Velocity throttle booster, DBA 4000xs rotors, Vibrant Performance catback, Synapse BOV & charge pipe, Hancook V12 EVOs 4 SHOW: DCT paddles, cusco strut, piano black trim, Mtech bumper, aero lip, 19" Miro 111's, angel eye, black: window trim, side mark, kidneys
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      09-01-2012, 06:32 PM   #3
enrita
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Mine does the same, got better after changing all vacuum lines and canisters but still there. Doing it with all tunes and stock.
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      09-02-2012, 08:11 PM   #4
JamesM3M5
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Sounds like lean surge. The pre-cat O2 sensors may be aged out and reading richer than actual. This will force the ECU to lean out. My car manifested similar behavior as a lean misfire at very light load and idle. Changed both pre-cat O2 sensors and cleaned MAP sensors.
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      10-30-2012, 09:10 PM   #5
tmurphy2
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UPDATE: turns out there was a leaking solenoid that was causing this issue. Smoke test showed this, just a heads up for anyone seaching this with a similar issue in the future
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      10-30-2012, 09:11 PM   #6
tmurphy2
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Quote:
Originally Posted by JamesM3M5 View Post
Sounds like lean surge. The pre-cat O2 sensors may be aged out and reading richer than actual. This will force the ECU to lean out. My car manifested similar behavior as a lean misfire at very light load and idle. Changed both pre-cat O2 sensors and cleaned MAP sensors.
this is an issue i am having now! does not cause surging but my cobb is showing me codes for this, good looks.
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e92 335i sport[/b] 2 GO: Cobb AP Stg 2+, Macht Schnell DPs, Injen intake, Spearco FMIC, Velocity throttle booster, DBA 4000xs rotors, Vibrant Performance catback, Synapse BOV & charge pipe, Hancook V12 EVOs 4 SHOW: DCT paddles, cusco strut, piano black trim, Mtech bumper, aero lip, 19" Miro 111's, angel eye, black: window trim, side mark, kidneys
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      10-31-2012, 01:48 AM   #7
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Quote:
Originally Posted by tmurphy2 View Post
UPDATE: turns out there was a leaking solenoid that was causing this issue. Smoke test showed this, just a heads up for anyone seaching this with a similar issue in the future
so the issue is gone now? did you change the solenoid? or was it the line?
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