My boost would act crazy at idle.
Seemed fine under load.
Don't know why tech determined upper tensioner ng.

questions then.. to determine how they figure out its the belt?

Did your car

a.) Hit boost.. then dump it??
b.) If not.. did it always just go all over the place without some sort of a pattern??
c.) how they come to the conclusion that it was the tensioner or the belt ?? (troubleshooting)

a. No, it didn't do this.
b. No, it didn't go all over the place without a pattern - it had a pattern. The trend was OK, just jumpy. For example under WOT the gauge would jump around between two and ten lbs.
c. The shop didn't conclude anything other than the tensioner looked OK.

The readings just jumped around very erratically. When it first started doing it I had the dealer service shop look at it and they said the gauge needed replacing (ie the instrument panel) So I had sort of just 'lived with it' for a while. Then, when artk'* post stated that his similar problems were resolved with a gatorback and tensioner installation, I took a look at mine. The belts were in much worse shape than I had expected (lots of cracks and a glazed appearance on the tensioner side). I checked my records and I had never replaced them. The tensioner appeared OK to me. I used my breaking bar and socket to move it around and it seemed to have tension. So I asked my mechanic shop to replace the belts and take a look at the tensioner. The shop said the tensioner was OK.
_________________
97 White SSEI..
Maf screen removed.. gutted airbox.. 4" dryer duct under fog light to duct cold air and force air into airbox ( Removed ). 180 Thermostat. custom "Pontiac" neon sign on trunk
Manual headlight kill switch
Alternating Flashing Fog Lights
NGK TR55'* plugs, Accel 8.8 Wires, GatorBack Belts

so my thoughts would be the belt was slipping terribly bad under heavy load...possible i spose.
Those pesky tensioners, mine ate like 4 of them, all replaced under parts warranty!
The gatorback is a good choice too..

This was a great thread, guys. Good work on this one, and Stever, damn glad you got through it with just a belt. Funny how a glazed belt can make it look like a bad MAP sensor. Something to file away for future reference.

I was amazed that all it was was the belt! It sure is nice that it works good now! Now if only my HVAC wasn't shorted out and my rear door would unlock. I did fix the charging system with a new "replaced under warranty" alternator though. Seems like the car is falling apart all of a sudden - but after cleaning my MAF sensor (per directions on another thread) my gas mileage has gotten lots better (up to 28.25 on my trip yesterday!). Thanks for everyone'* help!