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Old 09-09-2018, 06:28 PM
dwilliamscto dwilliamscto is offline
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Join Date: Sep 2018
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Mein Auto: 2008 335I
335i N54 engine caughs/stumbles and RPMs jump up and down

2008 335i N54 with 190K on it recently had general service now its undrivable
BMW had it for 2 weeks said it was LPFS sensor and HPFP they changed both and no change in the problem, now they want 175.00 per hour 5 hr min to "play around" to find what they think is an electrical problem.


oil change
New OEM parts
VANOS solenoids (both)
Crank position sensor
Cam position sensor
LPFS sensor
HPFP
EKPS
MAP sensor
TP sensor
Plugs
Coils

now she idles mostly ok,but stumbles and RPMs go crazy every once in a while (NO ODB codes)

If you push on the Gas and hold it at 2k or 3k in a few seconds she will cough and stumble and RPMs can drop to almost ZERO and switch up as high as +5k

the yellow "!" will appear check engine flashed on and off

If I check codes at that point nothing.


If I do a few WOTs it will flash the "!" and the check engine and might get ABS and Traction control light and LIMP mode. In OBD NO CODES!!
Now once she throws the LIMP mode engine symbol she will not stumble any more.
I can do quick WOT or slow build to WOT and nothing goes wrong

While running INPA looking at realtime data on VANOS what I am seeing when the problem occurs is:

inlet starts at 124.9 and will start bouncing down as low as 60
outlet start -130 and also runs thru a multitude of adjustments
I also see voltage to the fuel pumps swinging between 12 down to as low as 7
when LIMP mod hits sometimes DME will post a 3100 with 2a98 2a99


Once in LIMP mode if I watch INPA live data for VANOS no of the values are changing
inlet static at 124.9 and outlet at -130.

At this point I can WOT quickly or slowly press up to WOT and she never stumbles or coughs at all.

So WTH does this point at as the root cause of this problem?
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2008, 2a98, 2a99, limp mode, n54, vanos


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