I have a 1999 F-150 pickup with a V-6 4.2L engine.  It has the original
engine with about 132K miles on it.

Until the last few days, it turned over pretty much the first crank.  It
still turns over very quickly when it's cold, like first thing in the
morning.  But after driving for a while and then sitting for a half-hour
to an hour, the next startup takes longer, like 3-4 seconds of cranking,
for it to turn over. In other words, cold - no problem.  Semi-warm -
problem.  It also starts immediately right after shutdown, probably
because there's still fuel in the line.

In response to this issue, I changed the air filter last weekend (it had
been a while), but it didn't help.

Since the problem appears to be temperature-dependent, could it be a
fuel pressure sensor or regulator?  A relative suggested that I get a
tune-up, but the truck seems to run pretty smoothly once it starts - in
other words, nothing appears to be missing.

Any other reasonably cheap things I could try?  Is there any good way to
diagnose this electronically?  There are no check engine lights that
I've seen.

Thanks,

tmac