Looking for some input here on an issue that popped up last week on my wife’* 01 SSEI. Car had a cold starting problem that was do to a bad crank sensor, replaced it and made it worse "like a cold diesel", bought a GM one and now it starts fine. Around this same time it picked up boost related problem. When the engine is up to temp in WOT and above 4k on the tach the boost goes over 10psi and it misfires or detonates. The power falls off hard at this same spot before you can hear anything inside the car. If you back out it and keep the boost under 10psi it clears.
I checked a few things today like the sc oil level "a little low" and the bypass actuator which I can see moving when you snap the throttle. It had set a couple codes P1274 and P0300 when the bad crank sensor was in there, and we noticed cylinders 2&5 misfires on the scan tool just before it set a random misfire code. We swapped out a coil off my other 3800 and it made no difference. After I replaced the second crank sensor Friday it started up and runs fine but this same high rpm problem remains.
Other things we checked were the PCM plugs in the air box, all the vac lines on the engine and ran a couple tanks of injector cleaner through it. Can't find anything out of the ordinary and no other codes are showing up. It set another code today but I have not pulled it yet. I don't recall the boost ever going above 10psi before this started. Was thinking of changing plugs and wires but my experience tells me its computer related by the way it acts. The car is bone stock and runs fine the rest of the time.