BITRRBO

So my search for a solution to this problem still continues. I started the original thread on AZ a couple years ago, I figured I'd also start a new one here in hopes of getting some fresh ideas. Here is a link to the original thread if anyone wants some background info:

http://www.audizine.com/forum/showthread.php?t=139876

So basically I have been experiencing this slight surging/chugging sensation for a while now (~2yrs), which seems to directly correspond to fluctuations in my VAC (as seen in the videos below). It seems to happen intermittently and doesn't matter if the car is hot or cold; full of gas or not; etc., etc. It does, however, seem to get much, much better (if not completely disappear) when ambient air temp is below 60 deg. (F). For instance, it was 55 deg. (F) this morning and the car didn't act up once even though it has been driving like **** all summer.

And here are a few video clips I took with my digital camera so you can see what is happening:

http://www.youtube.com/watch?v=5DG8827TB8o
http://www.youtube.com/watch?v=eT5cx...eature=related

In an attempt to find the problem I've replaced/tested/tried all of the following, with little or no change in overall behavior:

1. Multiple pressure tests at a local shop AND on my own (w/ soapy water) a minor leak found at the bottom of the Y-pipe (fixed)
2. Replaced the TBB
3. Replaced the DV's and rebuilt several times (cleaned, greased, swapped springs, etc.)
4. Realigned the Throttle Actuator Valve (several times)
5. Replaced both the fuel & air filters
6. Swapped out the MAF, ICM's, and N75 w/ new ones
7. Cleaned MAF w/ entire bottle of MAF-cleaner
8. Replaced all the plugs twice (Iridiums, then Side-Fires) and coil packs w/ new Meyles
9. Resistance-tested all O2 sensors; all of them around 10.4 Ohms (<than 20 is still good)
10. SeaFoam treatment to intake & fuel tank
11. Bypassed the N249 valve and replaced the 5-Way Check Valve that connects it it
12. Replaced all the turbo inlet & outlet hoses w/ the Zena Racing kit and new clamps (except the first two turbo outlet hoses)
13. Obviously logged the car at nauseum, sometimes finding misfires, other times nothing

Despite the rough idle and slight chugging in VAC (cruising speeds), the car still pulls pretty hard at WOT (although a recent dyno session had my A/F around 13 : http://www.audizine.com/forum/showth...nce+dyno+Stage)

Unfortunately my current diagnostic methodology of replacing parts via "trial & error" has become exhausting and expensive... I have been seriously considering a different tune, but the problem seems to exist whether I'm in chipped mode or stock mode; leading me to believe its not necessarily tune-related. I also don't think it's mechanical (e.g. bent valve, low compression, bad wastegate, etc.) as the problem comes & goes as it pleases. Therefore I think it may be either electronic/sensor related, but IDK for sure.

Any thoughts/help/guidance is appreciated...

TIA!

NefMoto

You should data log as many sensors as possible and look for strangness.

BITRRBO

Okay... Is there something that I can compare my data to?

NefMoto

If you data log your car and post the log, people will give you a hand looking at it.