Bad stepper motor = boost problems?

[4rsfed]

Hi, I recently took my car into the dealer to get scoped out because it has been running terrible when I floor it. They told me that the stepper motor is bad, and that I have a worn turbo (excessive wear between fins and housing).
When I floor it the car seems to pull good until about 3-3500rpm and then it falls on its face and leaves a nice trail of black smoke behind.
I have 3 questions.

1) would the stepper motor make any difference to how it runs under acceleration? or is it more at idle that it works.

2) would the problem be from the worn turbo? or would the worn turbo just make it not build as much boost as normal?

3) if it's not either of these, what could the problem be?

The car is completely stock.

 

[DJYoshaBYD]

Well, falling on its face sounds like a boost leak.(FYI, you probably shouldnt go to the stealership unless you absolutly have to.

www.vfaq.com --- Go there and it will tell you how to make the tester and use it.

The smoke sounds like the oil seals in the turbo are bad, you can have the stock turbo rebuilt for next to nothing, like 75 for the machine shop to balance and polish your turbo internals and aboout 120 for the rebuild kit and its soooo easy. Again, vfaq.com tells you how to do it.

Do the boost leak test and check the turbo for shaft play, take the intake off, and grab the compressor wheel and try to move it up, down, left, right, in, and out. It shouldnt move in any of those, it should just spin.

Also, check your intake piping and intercooler for oil, that will tell you for SURE that it is your turbo.

Good luck.

 

[bling5tatus]

Maybe your turbo had excessive "play" between the fins and the housing, but the housing isn't such a "wearable" item.

I'd boost leak test your car.

 

[DJYoshaBYD]

^^^^ exactly... that doesnt happen unless your thrust bearing in the turbo are ###T.. .. boost leak test..

http://vfaq.com/mods/ICtester.html

heres how its done..

 

[4rsfed]

Hey thanks for the replies, I haven't gotten a chance to do a boost leak test yet, but it will be done by the end of the weekend.
I did check for shaft play and there is a little bit of up and down, maybe less than a mm but zero in and out play. Would it make a difference if the turbo is hot or cold?
And there is no oil in the IC lines.
As far as the smoke goes, wouldn't it be smoking blue if it is an oil seal? It is black smoke so that means it is running way too rich right?

Any more suggestions are appreciated and I will post back with the boost leak results
Thanks