Method and system for spark plug cleaning

A method, comprising:

• operating an engine of a vehicle while the vehicle is in a pre-delivery state at an assembly plant, including discharging a spark plug ignition coil according to a first spark schedule responsive to an indication of spark plug fouling while the engine is fueled;
• while the vehicle is in the pre-delivery state, intermittently discharging the spark plug ignition coil according to a second spark schedule, different than the first spark schedule, while the engine is unfueled responsive to a request for an engine start and also responsive to a request for an engine shutdown, regardless of the indication of spark plug fouling;
• operating the engine while the vehicle is in a post-delivery state outside the assembly plant, including discharging the spark plug ignition coil according to a third spark schedule, different than each of the first spark schedule and the second spark schedule, responsive to the indication of spark plug fouling while the engine is fueled;
• and
• while the vehicle is in the post-delivery state, intermittently discharging the spark plug ignition coil while the engine is unfueled according to a fourth spark schedule, different than each of the first spark schedule, the second spark schedule, and the third spark schedule, responsive to the indication of spark plug fouling while the engine start is requested and also responsive to the indication of spark plug fouling while the engine shutdown is requested, each of the second spark schedule and the fourth spark schedule including a smaller amount of spark advance during the engine start than during the engine shutdown.