hi there i see quite lot of these.ive had low turbo boots caused by the egr valve sticking open,also if its got the duel throttle body then ive had the flaps stick shut or open in the vacuum diaphram part causing boost pressure issues.theres a solenoid on the front on some and the drivers side on the others that fail,it controls wastegate opening.watch for the little plastic t piece near the oil filter,they crack and drop off vacuum to the boost solenoids.