problems

[exiletalon]

I have has this problem for a while. I hit some sort of fuel cut at 3500-4000 rpm. what stumps me is, I pulled the engine to do some work. I decided to install a newer lower mileage engine (97') in its place. Even after the swap, I still have the problem. What could it be???- car is a 95' TSI AWD, 97' GSX motor

 

[DSM90AWD]

I have has this problem for a while. I hit some sort of fuel cut at 3500-4000 rpm. what stumps me is, I pulled the engine to do some work. I decided to install a newer lower mileage engine (97') in its place. Even after the swap, I still have the problem. What could it be???- car is a 95' TSI AWD, 97' GSX motor

Have you noticed timing being pulled (due to knock), as that seems like the spool area a 18G would hit and possibly "spike"?

Could also be a boost leak or a fuel/misfire problem. Boost leak has an obvious remedy.
For the fuel/misfire, first check your plugs condition and re-gap if necessary. Second, take a bit of fuel out in that RPM range to see if that helps

 

[exiletalon]

Now, I fixed the 4000rpm cut whatever. But it studders at 2000rpm now, then it revs freely ot redline. I donno, idle at 900, rev it 100% throttle, and it raises to 2000 rpm- sits a sec, studders, hesitates, then 2500rpm it revs all the way up fine.

I do have an exhaust leak - my flex pipe in the down pipe has a rather large gash!
maybe that could cause it?