What does obd1 codes number 12 33 35 45 mean for 1990 pontiac grand prix

12 means it is in diagnostic mode
33 MAP or MASS AIR flow sensors
35 Idle air speed motor
45 is rich exhaust.

Check all the wires on the MAP/MAF device. Make sure the they are connected well. Check the ground points. You can unplug the connection with the car running to see if the engine smoothes out. IF it does then it probably needs new sensors.
The idle air speed is the same thing. Check the wires. Remove it from the manifold and make sure it is clean. Put it back on.
The oxygen sensors have a fixed lifespan and you should think of them like a light bulb. They get worn out about 60000 miles. Short life if they are subject to fuel addatives.

These are your OBD 1 Diagnostic Trouble Codes

DTC - 12 No distributor reference pulse (diagnostic test active)
DTC - 33 MAP sensor circuit error (signal high indicating low vacuum)
DTC - 35 IAC problem or idle error
DTC - 45 Oxygen sensor error (rich condition indicated)