You guys are pretty reliant on the electronics for diagnosis. Probably reasonable place to start since you have it available...not point in speculating until you have collected at least a basic dataset.

Assuming no ability to pull data, first thing that came to mind based on symptoms was fuel system. Able to deliver at low demand levels, under heavy driving conditions initially able to deliver, then pressure drops as flow inceases. Might even feel like cycles of full power with sluggishness in between.

Would love to hear what the resolution of the issue is...

 

I am having the same problems with my turbo. The car keeps jerking on and off, although it has never stalled. Under full load there are no problems but as soon as I slow down the problems begin. I have gone through 3 MAF's and now have the Hitachi. The car had a gt640 kit and now has a gt700 kit. I have no idea what the problem is but it's not the MAF. Possibly the throttle body. I have been working with Todd and still have not been able to fix the problem. someone please help!!!

 

Just a couple of other thoughts, since we don't have data logs....at what rpm are you seeing the symptoms (e.g., what is the idle rpm?)? Do you have an aftermarket clutch and LWFW? How about fuel system...do you have 5 bar FPR (a real one not just one with the label on it). What is your environment? Altitude?

Erock, yours sounds different than the OP. I suggest you get your idle adjusted via the ECU program.

 

I'm gussing the problem is just off idle...