Ignition coil
crank sensor
top plates (strut bearings)
fuel line leak
starter
the dash is rising (cheap assembly)
so far no head gasket problems :)
Apart from these problems the car is #1 I never had a critical issue with this car The 3.1 engine are a mass produced block,so expect the same problems you might have with your sunbird or someone elses
chevy cavalier or beretta or any GM model car that had the 3.1 from '89 to 96 (multi port or SFI) On the brighter side its AMAZINGLY QUICK because the engine suits the bodies weight. the 3speed is the only option available apart from the rare 5 speed ONE rule of advice do not overheat these cars change and flush your coolant religiously keep that powerplant cool.
I have a 1991 pontiac sunbird GT with the v6 3.1 l engine, manual 5 speeds, and I love the performances. I changed almost every part on my car expect for the engine and transmission, wich stills in excellent condition after 218 500 km, I have lots of probleme with frame also, but I have to admit that the car has 15 years... so 15 winters, with snow, calcium and every bad things for a car. I DISLIKE the braking capacity. But if I had some money i'd surely buy an other sunbird in better condition with better milleage.