87 2.8L Camaro, Car stumbles on acceleration. New plugs, wires, cap, rotor, pickup and module,(all OEM parts), base timing in bypass 10 degrees, tps .60 volts. When throttle is snapped open with timing light on engine, timing RETARDS off timing tab, engine pops back in intake. As RPM increase timing advances to 23-24 degress on mastertech scan tool @3,000 rpm. Have scoped MAF, O2, TPS can not find cause, any help?