Service engine soon light on. 1999 Pontiac Grabd am SE

Service engine soon light on. 1999 Pontiac Grabd am SE What could it be? We just replaced the crank sensor, starter, alternator, fuel pressure regulatory, battery was good still, front brakes, rear wheel cylinder both. Replaced oil gasket with new also change the oil with new oil and filter, replaced coolant temp sensor, PCV Valve, the medal part that is on the PCV valve. That runs from the PCV valve towards the back of the engine. All new 4 tires. Still a little rough idle, as well runs a little rough until it warms up., o2 sensor not long ago, the one behind the engine. 1999 Pontiac Grand Am 4 Dr SE Sedan Maintenance & Repair

Service engine soon light on. 1999 Pontiac Grabd am SE What could it be? We just replaced the crank sensor, starter, alternator, fuel pressure regulatory, battery was good still, front brakes, rear wheel cylinder both. Replaced oil gasket with new also change the oil with new oil and filter, replaced coolant temp sensor, PCV Valve, the medal part that is on the PCV valve. That runs from the PCV valve towards the back of the engine. All new 4 tires. Still a little rough idle, as well runs a little rough until it warms up., o2 sensor not long ago, the one behind the engine. 1999 Pontiac Grand Am 4 Dr SE Sedan Maintenance & Repair