First drive - bogging down

Post Mon Sep 17, 2012 6:21 pm

Took my rebuilt 325i out for its first spin this evening! First time it's moved under its own power in over a year, and this is with a replaced M20B25 engine.

First impression is that it's bogging down. It's hard to start when cold (crank crank crank, almost until the battery is flat, before it coughs into life). Once driving it will really chug and almost stall when you press the pedal before revving all the way up to the red, and it does that at both cold and hot.

From hot it starts on the button, and the idle is steady at ~600rpm with no fluctuations. New dizzy, rotor, sparks, blue plug, rebuilt injectors and all oils and filters replaced.

WD40 was sprayed around all the intake hoses, and no sign of any leaks, although the exhaust does have a small leak.
So, is this likely that it just needs a good drive to clear it all out and learn the settings, or is there a chance of a more serious problem?

Post Mon Sep 17, 2012 6:31 pm

have you read the wiki ? must be something on there

a decent place to start is to make sure the TPS/ICV and AFM are all doing their job ?

Post Mon Sep 17, 2012 6:46 pm

The AFM was used on the previous engine (it has a 325i part number) as was the ICV; they're fine. Also did a compression check and got between 12.7-13 bar on all cylinders, so that's good too.

I just want my beating heart put to rest that there's no serious issue with the motor

Post Mon Sep 17, 2012 7:37 pm

I had similar problems with mine after a rebuild, my problem was a broken wire from the blue sensor.

Post Mon Sep 17, 2012 7:45 pm

Fuel pipes the right way around? Fairly common mistake

Post Mon Sep 17, 2012 7:54 pm

Wiki suggests checking the new blue sensor at the ECU plug,this is to eliminate any possible wiring faults.

All you describe points to blue sensor problems...

Post Mon Sep 17, 2012 8:27 pm

I knew it would be something simple. AFM plug wasn't on tight enough. Did another check of all loom plugs (starting with the blue plug) and that one made a satisfying "click". Got back in, pressed the pedal, VROOOM!!!!

Couldn't resist taking it for a quick spin. Ohhh, this thing is awesome

Post Mon Sep 17, 2012 10:21 pm

Good stuff..! I thought the m20b25 was awesome too... until I dropped a m30b35 in.!