PN 16017460 1987-90 MAP sensor
Bolted to a bracket on the passenger side of the motor between the throttle body and the valve cover. MAP sensor is mounted outboard side of the bracket, EGR solenoid is mounted inboard on the throttle body side.
A visual check of all vacuum lines, hoses, electrical connections, wiring, is a good place to start. Then troubleshooting. TPS? Other sensors? Air filter? Warm air blend door? Injectors clogged? Timing, and Tune? Not necessarily in that order...
Any chance of restriction in the exhaust? might check, but probably something simple. Fuel pump at the worst. Good wrenching in there!