[mark houghton]

My first thought would be to look for a dislodged O'ring at the intercooler. It may have be been leaking and about to go earlier, then after your last hard run it probably tore and the boost blew it out of place. Had that happen to me once; the car would not idle and would stumble and run pig rich with about half the power it should when on full throttle and building boost. If indeed you did have a leak earlier and attempted to adjust with the mixture screw, then of course you'll find your mixture wrong once you fix the leak.

Pull the IC, take a look....it can't hurt and doesn't take much effort. Look especially at the O'rings from the up-pipe from the turbo, most common failure point. Also make sure that all IC and turbo mounting points are secure so everything stays lined up properly and doesn't move when the engine torques.