I changed coils,module wires and plugs,,still misfires.

I changed the coils the module under coils all plug wires and the spark plugs. Under normal conditions when an engine is missing it wont make the Tachometer jump and quiver,,this situation it does. I took Dash cover off and replaced bulb for service engine soon and that now functions correctly and is on . I have tried to reset ECM and depressed brake pedal with battery disconnected and then when battery is connected I have slowly pressed down on throttle pedal with ignition on and that didnt help either. I did notice that when it takes its fit ,,if the air conditioner is on it cuts off if that helps any,,,at this point now that service engine light is working Im thinking of taking it to someone who has OBDI scanning tools ,,I dont know what else to do.