Won't start after warm up.

I just purchased a 2002 Lincoln LS. Shortly afterwards I noticed that if I drive it for 20 mins or so and turn it off then try to start again all it will do is crank over. It takes several attempts and sometimes waiting 10 - 15 minutes before it will finally start. It will aslo cut out by jerking slightly sometimes as I'm traveling. I was told it may be the primary fuel pump. I replaced the primary pump on the passenger side with a new one. Still have the same problem. As long as it has been sitting for a period of time it will start up just fine or if I only drive it for 10 mins or less it will also start fine. It's only after a 20 min or more driving where I have the problem. The secondary pump was also mentioned as a possible problem but I thought as long as there is fuel already on the primary side that shouldn't have any bearing. I make sure to keep the RPM's up a little as I stop in traffic becasue it did die once on me and made a mess of traffic until I could get it started again. Any help would be gratefully appreciated.

It's probably your IAC (aka Idle Air Bypass Valve). It may be sticking when hot.
To test for this, the next time the engine is hot, try to restart it by holding the gas pedal about 1/4 the way down before and while starting. If it starts okay that way, the IAC is the problem. You can try cleaning it, but most likely it will need to be replaced.

It's probably your IAC (aka Idle Air Bypass Valve). It may be sticking when hot.
To test for this, the next time the engine is hot, try to restart it by holding the gas pedal about 1/4 the way down before and while starting. If it starts okay that way, the IAC is the problem. You can try cleaning it, but most likely it will need to be replaced.

Thank you for the advice I will give it a try in the morning and see what happens !!