Engine Controls - Tests W/O Codes: Symptoms: Backfiring

Check for vacuum leaks.
Ensure ignition timing is correct.
Ensure timing belt or chain has not jumped.
Check distributor (if applicable).
Ensure fuel injectors are not leaking.
Check spark plugs and plug wires.
Check ignition and coil circuit.
Check crank and cam sensors (if applicable).
Check TP sensor and connector.
Check exhaust system.