Help diagnosing boost problem...
 

I need some help figuring out what's causing my 951 to run poorly. Here are the details:

First symptom was a stuttering under acceleration. This was intermittent at first but got gradually worse throughout the day. I eventually observed that it only occurred under boost - it would start stuttering as soon as the boost guage went above atmospheric.
I thought it was a bad bypass valve so I replaced it (with the aftermarket unit from Paragon Products). At this point, the symptoms changed slightly. The car would boost up to 1.2 on the boost gauge quickly, but wouldn't go over that without some extra prodding. The stuttering did not occur until going over 1.2 on the gauge.
I took another look under the hood and discovered that the vacuum line on the fuel pressure damper was disconnected. After reconnecting the vacuum line, the symptoms are similar except that now it won't go over 1.2 unless it's almost at full throttle.
Any ideas where to look next would be greatly appreciated.

did you check the 3 hoses that go to your cv?

build a KLR diagnostic LED and see if the KLR is giving codes. i built one for less than 5 dollars.

i had a similar problem. turned out to be my DME.

also, check really thouroughly for other vacuum leaks. also, if the CV fails, or is unhooked from its electrical connection, it will usually fail open, making your wastegate start opening immediately.

how is your accelleration?

I haven't had time to check the vacuum lines thoroughly, and I probably won't until next weekend. I'll look into the KLR blink code LED. Acceleration seems ok at part throttle, and I think it would be decent at WOT if not for the stuttering.

what about your blow off valve? could it cause this?

That was my first guess. I already replaced it.