My truck has a really hard start but not once it's warmed up. What could cause this ?

i have replaced the spark plugs just
recently. And changed the oil. The
truck turns over a lot before finally
starting at first. And when it does it
just is boggy and then catches after
a second or two. If I drive it to say
the gas station and I get out go in
quick and come back out it starts
fine. But if it sits for more then 30
mins it will have a hard start again. I
got the code for a bad tps so I
changed that and then immediately
after got a code for the 2nd cylinder
misfiring. I cleared it and it hasn't
come back on yet. Been 2 days now.
The truck runs fine as well when it's
going. Sometimes idles close to 500
but then will bounce back to 1,000 if
I sit long enough or tap the gas
pedal.