I have a 97 F150 XLT SC 4.6 V8. This morning i took the truck out for a quick errand, runs fine. Later on I started it and ran really rough. I started and it several times and still ran idled rough. Four hours later I started it and idled rough then smoothed out but check engine light is now on. I did have to crank it a bit longer to start. What can be wrong. Please help before I take it in.

 

I had the "check engine" light come on not long ago - it was 1 of the o2 sensors just down from the cat & I had it replaced under warranty even though there isn't any warranty left! I got the impression the sensors are a part they can turn back in so they did it as a warranty job. I'm not positive though.
Any chance you got some bad gas? Maybe ther ewas water or dirt in it.
It could be a sensor or possibly dirty fuel injectors. Have you used any injector cleaner? It probably wouldn't hurt to throw some in - I was told the "expensive" STP cleaner is the best - I guess it's around $5 if I remember my advice correctly.
Good luck - I hope it turns out to be something very simple & inexpensive for you!

 

It could be a zillion different things or a combination of a zillion different things.

The first time I ran my truck WOT in a quarter mile it had a really rough idle afterwards. It scared the devil out of me. The engine's computer smoothed the idle back out within a couple of days. I could feel it gradually get better. However, the check engine light never came on.

Its probably something very minor, bad sensor, loose wire, something needs to be cleaned, etc. If the rough idle continues I would definately have a mechanic look at it. Good luck.

 

I have the same truck as you. I would suspect the IAC(Idle Air Control) is dirty/worn. It's the bright chromed 'can'(a little bigger than a 35mm film cannister). Take it off(easy) and try cleaning it with a brush and carb/brake cleaner. Shake it back and forth and see if the inner valve rotates back and forth freely--if it won't, replace it($45?).

You may need to replace the fuel filter--how long has it been in? i think 15,000 miles is its limit.

 

Thanks for the help. I drove it to my mechanic this morning. It ran fine (check engine light on) as if nothing happend but as soon as I drove into his shop, the check engine light went off. He was still able to retreive the code. It came out with an EGR code. Told me to drive it and wait for the light to come on again. He said its probably a carbon deposit that clogged it and broke loose. My option...clean it out or replace.