BITRRBO

Hello Everyone. I'm a long-time reader/lurker, but never really posted here. I've been trying to get some help trouble-shooting this issue on AZ for a while now, but I think I might have better luck here if you know what I mean (hopefully .

Here is a link to the original thread if anyone wants some background info:

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

And here is a video clip I took with my digital camera last year so you can see what is happening:

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

Essentially 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 above). 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) the other day and the car didn't act up once, even though it has been driving like **** all summer.

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

• 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)
• Replaced the TBB
• Replaced the DV's and rebuilt several times (cleaned, greased, swapped springs, etc.)
• Realigned the Throttle Actuator Valve (several times)
• Replaced both the fuel & air filters
• Swapped out the MAF, ICM's, and N75 w/ new ones
• Cleaned MAF w/ entire bottle of MAF-cleaner
• Replaced all the plugs twice (Iridiums, then Side-Fires) and coil packs w/ new Meyles
• Resistance-tested all O2 sensors: all around 10.4 Ohms (<than 20 is still good)
• SeaFoam treatment to intake & fuel tank
• Bypassed the N249 valve and replaced the 5-Way Check Valve that connects it it
• Replaced all the turbo inlet & outlet hoses w/ the Zena Racing kit and new clamps (except the first two turbo outlet hoses)
• 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 sometimes:

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 the "tune". I also don't think it's internal or 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!