Difficult Start

Ensure sufficient secondary spark is available.
Check air induction system for cracks or restriction.
Check airflow sensor plate rest position.
Check cold start valve for leaking (engine warm).
Ensure vacuum hoses are not disconnected or damaged.
Ensure fuel system pressure and volume are correct.
Ensure fuel system residual pressure is correct.
Ensure fuel injector operation is correct.
Ensure EGR valve operation is correct and that valve closes completely (if equipped).
Check for cracks or poor connections at throttle body.
Check for cracks in air induction system.
Ensure ignition and valve timing are correct.
Check ignition coil primary connections and wiring harness.
Ensure ignition coil resistance is within specification.
Check air temperature sensor operation.
Check coolant temperature sensor operation.
Ensure electrical harness and connectors are not broken or loose.
Ensure that ECU or ignition control unit has correct voltage supply and is properly grounded.
Ensure engine has sufficient compression.