When you get the trouble codes read be sure to write them down so you can post them here.

The 3800 II'* are pretty solid motors, if taken care of properly.
The main thing is keep up to date with servicing fluids, and check to see if the lower intake manifold is aluminum framed, or nylon/plastic framed.
If plastic framed then in the future plan to have the upper intake manifold removed/cleaned or replaced, and have the lower intake manifold removed so the plastic gasket can be replaced with a redesigned aluminum framed gasket, have the old EGR stovepipe removed and replace it with a redesigned/reduced diameter one from Dorman, and also have the coolant elbow replaced with an aluminum elbow.
For now it should be fine, just make sure you, or your son pays attention to the coolant levels, if it ever seems to be needing topping off more than usual then come here, start a thread on the issue, and we will help you out.

Back to the EVAP problem, look for the large wire loom near the rear passenger side of the engine bay, if you can find that see if any EVAP Tee'* or EVAP hose is coming out from it, I'll try to get a pic of what I am talking about if possible.
The loom should have the fuel injector wires coming from it, with my 96' PA that is how it is anyway.

Thanks all, still no luck. John01 after I disconnect the battery to clear service engine lite it comes back on within 7 miles of driving although engine runs very smoothly since cut off emissions hose was plugged with pencil and tape. Crap after one month of me working on this car with new struts, steering rack, body work on rockers to pass inspection etc. I can't resolve the P0171 code which is the only one outstanding and can't get a sticker. 7 months is a long time to wait for grandfathered emissions to get sticker which I knew was the backup plan but wanted to avoid it as the car will have to sit and that is not good for it. Some advised me to clear the check engine lite with an OBD II and Torque Pro app (total cost <$15) but others said they will know that you cleared them yourself and will fail you. Conflicting messages. The car looks great now and son is salivating but this code has us in a checkmate. Emissions suck pardon the pun.

Thanks all, still no luck. John01 after I disconnect the battery to clear service engine lite it comes back on with P0171 running too lean, within 7 miles of driving although engine runs very smoothly since cut off emissions hose was plugged with pencil and tape. Crap after one month of me working on this car with new struts, steering rack, body work on rockers to pass inspection etc. To add to the turmoil this car has the overdrive (4th gear) fried in transmission (very common problem) which was due to a known issue for this car and other GM models using the original soft steel overdrive shaft? I can't resolve the P0171 code which is the only one outstanding and can't get a sticker. 7 months is a long time to wait for grandfathered emissions to get sticker which I knew was the backup plan but wanted to avoid it as the car will have to sit and that is not good for it. Some advised me to clear the check engine lite with an OBD II and Torque Pro app (total cost <$15) but others said they will know that you cleared the codes yourself and will fail you. The car looks great now and son is salivating but this code has us in a checkmate to even take it out . Emissions suck pardon the pun.

Here Joe is some extensive information to review, about the P0171 code:
P0171 and P0174 - OBD-II Trouble Codes
Have you replaced the fuel filter & run some good fuel injector cleaner in fuel, like Chevron Techron concentrate?

Thanks. Considering nothing was ever likely changed on this car except for engine oil in 15 years bets are that the fuel filter is original too and I think I will try that next in addition to me finding where the former hose (where yellow pencil stop) goes to HVAC > canister. WHy it was ever cut or trimmed is beyond me. Hopefully it is not the fuel pump starving the thing causing too lean P0171. Should I try some SEAFOAM too in this thing for P0171?

Mike I don't think this car has electronic climate control looks to be manual but I could be wrong cuz I didn't think it had a Magnasteer RACK and it DID! Caused another delay.

OK I am confused am I chasing and looking for an EVAP or an HVAC controller with the cutoff hose which sucks in below:

I didn't see a vacuum hose back there so if anyone has a picture that would be great otherwise maybe I will go look at a junk yard car with a 3.8L that would show me where it goes.

Hard to tell where you are at by the photo.
Anyway to post a wider view from above showing where it is?
Here is a photo from my 97 Pk Ave looking in from the front for instance, does this help at all?

Soft Ride, you are looking straight down at the rear valve cover where the brake booster hose attaches to the fitting out of the upper intake in the rear....apparently there is a tee fitting.....he has it plugged so the engine idles.....that tee usualy feed the HVAC, but if the system uses all electrical actuators, then vac isn't needed and it usually just has a cap on it....

P0171, is kind of a misnomer......lean on Bank 1.....since the system only monitors with one O2 sensor, it'* actually monitoring Bank 1 and Bank 2.....

Two usual problems are, bad MAF or a vac leak, or it could be an Exhaust leak.....other possibilities, are clogged fuel filter, low fuel pressure, dirty injectors, etc.,.......

How does the car start cold? OK? any misfires rough idle? You replaced plugs(use OEM?), did you replace the wires too? If you didn't replace the wires, check the terminals of the coils for arcing.....make sure wires are going to the correct cylinders....does it run better when warm?