Just bought a 2015 3.5L ecoboost and there was a P0305 code indicating a cylinder 5 misfire. Found cylinder five and what looks like the “lock” that holds the wire harness onto to the top of the spark plug wasn’t engaged (the red slide tab). Cleared the code and started back up and no engine light. Could that have been the problem? I had the dealer do a used car inspection on it before buying it so they might not have “locked” that. I don’t remember the check engine light being on prior to bringing it in. Thanks in advance.

 

Seems likely.