I have a '91 Cavalier RS 2.2L Auto. Ever since I've owend it whenever you start it the oil gauge would go all the way to max (80psi) and when you drove around for awhile and stopped it would bouce around and just be real jerky. When ever you started to drive agian it would go alll the way back to 80psi. Now yesterday i started it and it just stays at/around 40 until you've driven it for about 10-15 mins and your coming to a stop, then it goes all the way past 0 and the 'check gages' lights comes on. I thought maybe i just needed my oil changed so I changed it but it's still doing it. any ideas? THANK YOU!

Check to make sure the sender is in all the way (not leaking). If its good, listen for alot of valvetrain noise. The 2.2 has ticks normally, you're listening for abnormally loud noises. If there is a ton of noise, check the pump, its probably bad.