I have an 88 IROC convertible, 305 TPI, automatic. When I accelerate heavy the service engine soon light comes on. I scan the car and it gives me Spark Timing . I have had the car since 2021. I have replaced with new AC delco plugs, wires, cap, rotor, coil, ignition control module, knock sensor. The light goes off when I shut the engine off and does not come back on. I am at a total loss on what to do next any help is appreciated.

Thanks
Steve