i have a 1983 pontiac bonneville with the v6 in it. it has less than 100,000 miles on it. it was running great, until we let it set for about 2 months over the summer as the air was not working and it is hot here (phoenix Az area).
we did a tune up (plugs rotor, belts, air, oil, and fuel filters, pcv, oil change, and timing) right before we parked it. it was running great and had no issues other than the a/c compressor being noisy.
it now starts fine and idles fine from cold through warm. but the second you put it in gear, any gear, forward or reverse, it just dies. you have to almost floor it to keep it running when in gear.
it also sometimes backfires out the carb while doing this. we have checked all the vacuum lines, both visually and via spraying wd-40 on the lines while running to see if the rpm change. we found a couple of bad lines and replaced them, but it made no real difference.
fuel pressure and volume also check out fine.
oh and there seems to be almost no brake boost. i thought this might be bad and maybe causing the issue, but i plugged the line, where it comes out of the carb base, and had the same issue.
any help or suggestions would be most appreciated. thanks in advance.

I can think of two possibilities, neither of which is technically Bonneville-specific:

1) The Torque Convertor Clutch solenoid is stuck on, which basically locks the engine to the drivetrain, as if you were in high gear at highway speed. Not sure if this should affect Reverse as well, but a malfunction is a malfunction.

2) You've got a massive vacuum leak, which is doing Gawd-knows-what to the ECM inputs; the computer may be getting no usable signals coming in and is operating in some kind of puke mode. Sorry about all the scientific terminogy there. When the engine is running (when you're in Park), do your ventilation controls work properly? If you dial up the Vent setting, can you get air to blow from the dashboard vents, or does it blow through only the floor vents or the defroster vents, no matter what setting you select? If you can't get Vent mode to work properly, you've got no vacuum in the system, and you'll want to check under the hood for busted or disconnected vacuum lines. Start with the black, round sperical booster reservoir on the firewall near the passenger'* side wheel well, and follow the lines from there.

That'* all I got... I'm guessing here, but see what you find out...

I'm going to lean towards a vac leak. Can you put a vac test gage on to see what you have? Did you check your EGR tube? That gets missed a lot when looking for vac leaks.

already did this, no leaks.....
we have checked all the vacuum lines, both visually and via spraying wd-40 on the lines while running to see if the rpm change. we found a couple of bad lines and replaced them, but it made no real difference.

we also disconnected the connector on the transmission that engages the torque converter lock, no difference.

we also just sold the car, so i guess we will never know. thanks for your help though.