Cranks Normally But Difficult To Start

Check for strong spark.
Check ignition timing.
Check Engine Control Module (ECM) ground and power circuits.
Check intake manifold vacuum. Vacuum should be more than 17.7 in. Hg at idle.
Check air filter element.
Check if engine starts with throttle 1/4 open. If engine starts, check for carbon deposit on throttle valve.
Check fuel pump operation while cranking engine.
Check fuel injector operation while cranking engine.
Check fuel pressure while engine is idling.
Check fuel system holding pressure.
Check spark plug condition.
Check engine compression.
Check terminal voltages of Mass Airflow (MAF) sensor, Throttle Position (TP) sensor, ignition coils and Engine Coolant Temperature (ECT) sensor at Engine Control Module (ECM).
Check for contaminated MAF sensor element.
Check Idle Air Control (IAC) valve.
Check if engine starts with ECT disconnected.