check for codes stored in the computer. for instructions do a search on this site for obdi codes. code 12 should be the only code you have.
The computer uses information from the Map and Coolant temp sensors in additon to engine RPM's. A diagnostic scan will be helpfull in troubleshooting sensor information.
Low MAP sensor output voltage= more spark advance.
Cold engine= more spark advance(normal)
High MAP sensor output voltage= less spark advance
Hot engine = less spark advance.
Detonation can be caused by low MAP sensor output or high resistance in the coolant sensor circuit.
poor performance can be caused by high MAP sensor output or low resistance in the coolant temp circuit.