I'm thinking that the ECU has to know that the engine is running in order to activate the assist solenoid when the engine needs more power under load. Your accelerator pedal tells your throttle sensor that it needs to open farther when you step down on it. Then the ECU will respond and open the assist or boost solenoid to compensate for the extra load being applied. Still thinking the holder is plugged. Just in case the ECU p/n's have to be exactly the same. You can't just change one over from just say a dual fuel unit. Part numbers would have to match.