F150 2003 start problem disappears as engines cools

Twice in the past 2 months my low mileage 2003 F150 (after Shutting down the engine for a pit stop) started but had a very rough idle. On the first occurance I let the truck sit for approximately 30 minutes and it started fine. On the second occurance I waited for 30 minutes but it did not start or started with a very rough idle with no acceleration. I had it towed to my mechanic and the next day he called to say the truck runs fine. He said there were no codes (whatever that means). In the old days I would say the truck was flooded but I don't think that applies with fuel injection. Also, the truck gets little use and may set idle for 2 weeks at a time and several years ago I had to have it retired because of corrosion. Could this still be the problem?

Most everything on a modern vehicle has a sensor that when it detects something not performing correctly will send a signal to the computer about the problem. The computer will hold on to that information as a code. Your truck didn't give a reading for any of those error codes is what your mechanic is saying. Until the problem gets big enough to produce a code, it becomes a needle in a haystack search for the issue.
I've had a whole host of causes for a similar problem over the years. The most common that didn't like to initially trip a computer code is a fuel pump going out. As it goes it can be intermittent and the fuel rail pressure sensor doesn't seem to want to give a code when it should. A clogged or clogging fuel pump as been an issue at times. Debris in the fuel tank stopping the fuel intake hose then moving away from it after no longer being sucked up and getting sloshed away from the intake from towing or a later startup and movement. A vacuum line broken in a bend that in certain positions stays closed and runs normal and from engine movement will open up and cause terrible running up to and including stop run and inability to start.
These are just a few of the things that I'd start checking if it was my truck. And when I say a few, there are hundreds of things from the above to loose wires, etc. that can cause these symptoms. All you can hope for is to have something permanently break, a code to help find it come up or you find it through trial and elimination.
Good luck.

Thanks 65comet. Sounds like you've been there before. Fuel pump or debri in the gas sounds most likely, maybe even water in the gas. This truck sits quite a bit from lack of use and condensate might be building up. I have a 78 F100 short bed that I use most. Wish these newer trucks were as easy to fix. Back in the day we sometimes put cloths pins on the gas lines to absorb heat to over come intermittent vaccum lock. The problem with the F150 gives the same symptoms.

I plan to put a can of Sea Foam in the tank hoping it helps.

Today's ethanol gas when it sits for a long time can cause a lot of water in the tank. I've taken off fuel filters that had only water in them. Any vehicle that doesn't use up the entire tank regularly should have a fuel stabilizer added to handle the water in fuel issue. I wish they would get rid of the ethanol mandate.

I use Staybill for all my small engine stuff and my outboard motor. Works well except for the outboard. My mechanic brother has taught me well about ethanol. All gas purchased by me in a portable container is first spiked with gas treatment. Guess I'll start using it for my seldom used F150. Thanks a bunch for your time and input.