Engine Has Rough Idle When Warm

WARNING: This page is about a different car, the 1995 Dodge Pickup and 1995 Dodge Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

Air in fuel system.
Poor fuel quality.
Low idle speed.
Leaking high or low pressure fuel line
Loose injector pump rear support bracket.
Restricted or damaged fuel injector.
Injection sequence does not correspond with firing order.
Low or uneven engine compression.
Incorrect timing or defective fuel injection pump.