[bmwe90320i-N46]

Hi all,


I replaced the engine in my 2005 E90 N46 320i, and ever since a problem has developed which involves starting rough and almost stalling.

HOWEVER if you turn the car off, and back on again it starts perfectly fine. Turn it off and on, rough start. Off and on, perfect start.

This goes in a cycle forever and is always consistent.


On my cheapie OBD2 scan tool it says one of the downstream O2 sensors isn't reporting any output (V = 0.000), which should be reporting V= 0.440 even if a sensor isn't plugged in during start up. I've been told downstream O2 sensors don't have any effect on vehicle start up as they only work when hot. The wiring and pins have been confirmed to be working on the sensor and harness side connector, so it isn't a wiring issue. Must be something software related?

I DON'T HAVE AN ENGINE LIGHT OR ANY CODES. ALL SENSORS AND THE CATALYTIC CONVERTER HAVE BEEN REPLACED.


I've heard people struggle with hard start ups after replacing spark plugs and they needed an "adaptation tune" or something like that to fix the problem, but I've got no idea what this involves! Is this BMW specific, or can any auto tuner shop do this?


Any help would be greatly appreceiated... thanks!