I've been chasing down a strange turbo problem in my car. Last Saturday I floored the car in 5th gear going about 50-55 MPH. The turbo severely overboosted and the ECU cut fuel flow. It did this twice, and I took it home and checked all the vacuum lines going to the wastegate and solenoid. It didn't repeat the fuel cut, but it boosts erratically now and still overboosts.

Basically, short boost build time (like from a stop) it underboosts, 1.1 Bar or so. Long boost build time (ie floor it in 5th and let it build up) it spikes to 1.7 and then tapers off to 1.4-1.5 and wavers there.

The car uses a stock ECU with a Works Rally P2 flash that's been on there for a year now. The BOV is a JDM MR metal full recirc (like stock) setup and no other significant mods. Any idea what's going on?