I just recently bought my 87 Iroc z with the 350 TBI. The car sat for about a year. Started occasionally. Previous owner stated there was a new fuel pump installed but the tech accidentally switched fuel lines. Says if the gas cap is on tight, it builds pressure and leaks gas out of the canister. Now I've noticed when I filled the tank, the canister would leak up until a half of tank. The car has a rough idle at times and sometimes shut off. Bucks going down the road then clears up. Also takes a few turns to start the car. Would the fuel lines being mixed cause all of this? Please let me know ASAP. Thank you

 

(you just said TBI but im assuming TPI based on title...)

I would get the lines plugged in properly to start.

Secondly, you could still have any number of reasons for your issue. Old leaky fuel injectors, bad fuel pressure regulator, weak ignition .. all sorts of stuff.