Miles on engine?
Idle vacuum, steady?
Has it been sitting, how long?
Aftermarket maf, computer stuff?
Been getting worse, or a new development?
Need more info to help!
Mods are not OE chip will need to find a new home in a box.
Old injectors need to go too.
Timing chain is Junk
valve springs Junk
35 yearly cars are not almost new.
My Cristal ball is broke and you will break this Buick too if not carful
Then O2 sensor, TPS (don't forget to set idle at. 45 full throttle at 4.6v.)
FIRST!!!! change oil and filter ADD ZDDP ADDITIVE! RUN THE ENGINE TO 2000 RPM AND HOLD IT THERE FOR 10 MINUTES! MINIMUM Before doing any idling!
Change radiator water/antifreeze.
Changed the oil and filter in Michigan and when I got home so 1300 miles two changes .I'm new to the turbo world but this car came out the year I graduated from high school yes I'm old ! But this car has been on my bucket list for ever
These cars were the first SFI motors, but they used the old stupid computer. Sensors, connectors and grounds are the biggest issues with these cars. Garbage in equals garbage out, with ALL computers.
Timing gear is a big deal, they dry out and crack/disintegrate with age not just miles. Sensors and connections too.
I would change oil often for a while so the fresh additives can work their detergent action on the interior parts that may have corrosion or shellac on them. It's cheap insurance.
Look at the fusible links at the starter, they use rubber insulation on them so if they get hot or melt, they will stink as an indication of problems. BUT that insulation dries out and cracks and falls off and can cause a short.