Bogging issues

[ppz3]

Hi everyone,

Been lurking for a while, on m3forum also, but sadly this is my first post.

I've been having an annoying issue with my car, where it will bog down if you apply throttle at low rpm, especially noticeable at neutral. This makes rev-matching pretty much impossible, and the car is noticeably slower to respond when driving normally. Also, if I go WOT at low rpms, there is a noticeable delay before throttle actually picks up, I know this is not typical use but it's where the problem is most amplified. Thankfully I have access to a sub 10k miles car that I can use as a reference and log from too, and I've been comparing the two.

Only 2 drivetrain mods I have is SSV1 with cats, and lightweight flywheel with sprung clutch. No tune yet since I wanted to fix any issues first. Motor has 40k miles.

I've swapped a lot of parts to try and pinpoint the problem, but nothing really worked so far. I've changed:

- Rebuilt vanos (luckily caught a broken tab at the same time)
- Adjusted valves
- Almost new injectors
- New coils
- New plugs
- Swapped crank angle sensor for a spare used one
- New top TPS
- Cleaned ICV
- Tried a known good MAF
- Persists on freshly reset adaptations
- Stable 50psi fuel pressure

I've tried to log a bit with testo, and you can see the issue on the 2 attached charts. There is a often a good half-second between the time the pedal is pressed and when the ECU applies throttle. The o2 sensor readings also appear a bit strange and inconsistent to me, while on the "new" car they are super stable and the two banks track each other almost perfectly, but I'm not sure what that could mean.

Sitting with engine off, the throttle bodies react instantly to the pedal, which I'm thinking would rule out tps\pedal\tb issues?

Anyone has any ideas or pointers on what I should try next?

[Slideways]

With those mods and no codes, it will most likely need a tune. Only other way IMO is to swap back the stock parts and test with the stock tune.

[ppz3]

With those mods and no codes, it will most likely need a tune. Only other way IMO is to swap back the stock parts and test with the stock tune.

You were more or less on the right track, as I flashed a stock M3 tune on the car and it fixed everything (the car is a Z3M). I don't know enough about tuning to figure out what was the issue, but looking at the maps in tuner pro they are quite different. I initially attributed the relative sluggishness of the Z3Ms to the 3.12 diff but after living with it for a while these problems became apparent enough that I thought it was broken. Maybe BMW did in fact detune these cars?

Anyway time for a real tune!