My boy completed the mpfi swap just fine. but the other day a loose connection caused the car to start spuddring and rev only to 3k the check engine light came on and the ecu was throwing code 4. He fix the connection and it fixed the spuddering. but the problem now is the check engine light is off but the ecu still throws a code 4 and the car doesn't feel as quick as it was before the loose connection. What could be the problem?

 

Try reseting the ecu!! Remove the hazard fuse from under the engine for like 20 seconds and put it back in and start the car and see if it's gone!!