1998 4 Cyl. automatic trans. rough idle while at stop light

When truck is stopped and still in drive, the idle is rough, almost shutting down at times, if I switch to park or neutral, it idles fine also runs fine when driving. New aircleaner, 89 ethanol free fuel. Thoughts/ideas?

 

Do the easy stuff first.
How old are the plugs? cleaned and gapped?
Air filter clean?
Sprayed the inside of MAF w/ specialty aerosol cleaner made for the purpose?
Sprayed the throttle body internals w/ SeaFoam while car idles?
Dumped Techron into the gas tank?
Fuel filter?
Is oil old or dirty?
May end up paying for an injector service cleaning.
Read any codes w/ a code reader? Write down the numbers and look them up.

This will get you started.

 

Try removing the idle speed screw.
It may have a bad "O" Ring.
Ace Hardware will have a new "O" Ring.