Engine issues, help me with where to start

[BMW2ner]

OK heres the long story.
At auto-x a week ago my car made one lap then it sputterd low rider style back to grid. After hours of messing around with the car and haveing no BMW guys around I came to the conclusion that it was my m30 afm. Because when I messed with the gears on it it would run for a few min then have the same problem. Eventually I got it to drive me home as long as I didnt go under 3k.
So I figured that the m30 afm was unreliable and I ordered a m20 afm (used) I put that on and let run for a few min. Went to rev it up and white smoke came out. I figured ok I still have the 19lbs in there so thats the issue. Let it sit for a few more min then reved it again, not gray but not to black smoke and sputtering and wants to stall.
So this weekend I want to take care of it. I'm thinking spark plugs, then o2 sensor (but it was replaced under 6k miles ago?), and put my 14lb injectors back in.
Anyother suggestions on where to start, or what my problem might be?

[7704ryan]

Not to be a downer or anything but as far as I know white smoke means coolant is burning somewhere. Maybe you just blew a head gasket. check your coolant to see if it's low. You could try a compression test too. Other than that I don't really know what to say other than bummer. :(

[BMW2ner]

I'm thinking white smoke as in running way rich cuz the 19s are still in

[yozsi]

I'm thinking white smoke as in running way rich cuz the 19s are still in

naw rich is black smoke. you sure the smoke isnt real light grey?

[BMW2ner]

its more of a light grey now that you say something

[euroshark]

Maybe the head gasket took a dump?

[bumpstop335i]

How have you adjusted your m30 afm? Did you tune it to your o2 sensor?

Did the replacement m20 afm have the same numbers as your orginal m20 afm? This is sometimes over looked.
Different variants of the m20 afm were made, like the ecu numbers. Some afm's go with certain ecu's.