I have a '99 F-150 4.2L with 124,000 mi. It has begun starting hard when it is warmed up and has set for 15-30 minutes. Plugs have about 25,000 mi on them. Plug wires are all in good shape. All computer codes check out normal and it runs fine after it does start. Have replaced fuel filter, ignition coils, and IAC but still has problem. Any ideas?

 

Try cycling the key a few times before you try to start it. The fuel pump may be bleeding down. It's supposed to hold pressure in the lines so it will start easier next time.

 

could it also be the fuel pressure regulator

 

Haven't seen too many fuel pressure regulator problems. Most of the time when they go bad gas gets sucked into the vacuum line and the engine runs VERY rich.