It throws the code while idling & the fuel trims at idle are:
Short term +20%
Long term +16%
At 2000 rpm the short term drops to 10%
At 2500 rpm the short term is right around 0%
This lead me to believe the problem is vacuum related & not a fuel supply issue.
Here'* a video - I'm going in!

Whoop..there it is.

I thought it was just the lower intake gaskets that fail.

...I hope the rest of it is stuck to the underbelly of the blower.

Some of the gasket was stuck to the supercharger but you can see 2 major leaks in the lower picture.

Here'* the fuel trims after the repair. Is the -11.7 within the normal range?

It'* a good thing we got in there and changed the lower intake gasket. Looks to me like it wouldn't have been much longer before coolant flooded the crankcase.

nodnod - looks like good timing on your part.
Now, the trim numbers that the 'gauge' software is reflecting is unfamiliar to me. Was this at idle? I'm also not familiar with the normal operating trim specs for the Bonneville. It'* certainly not stoichiometric. How long did it take you from start to finish?
What program is that which you're using?

I'm using the AutoTap software. All the readings were at idle. When the gasket was broken it was running lean at idle. The PCM then increases the fuel trimsto richen the mixture. When the trims max out (20% & 16%) then Code P0171 is thrown. I might change the O2 sensor & see what happens.

This was the first time I changed the gaskets on a 3800. I'd guess I spent 5-6 hours a day for three days. Probably as much time spent cleaning parts as actual assembly/disassembly.

your SC gasked didnt fail, its just stuck to the other side of the SC. totally normal when removing the charger for it to look like that

Lean bank 1 is not because of the fuel trims. Yes that code can set becaused of wacked trims, but that is not the only thing that causes it. Have you looked at the battery cables....remember another members nightmares....it 0171 was caused soly by the battery cables....

did you reset fuel trims....you Must do this if your going to get an accurate reading...-11.7 is not a good LTFT

Did you see the video & look carefully at the second picture. Oh yeah - & what about the results!

i've had that issue on my 98..the SC gasket cracked or was re-used..not sure but I had a massive vaccum leak which casued the car dealer to think the engine was on its way out.