96 Blazer idles bad

Sounds like a vacuum leak, check the lines from the engine to the 4X4, the ones that go from the drivers side to the interior controls and vacuum canistr and see if one has a hole or broken T fitting.

Also check throttle body butterfly for accumulated crud/soot. Look at IAC for same.

Clean out the idle air control valve and throttle body and see what happens

If tapping on the accelerator makes it come down, that is indicating a problem with the way that the throttle plate is seating. You may have a worn out throttle body causing the throttle plate to stick and bind. Here's what I would do.

You may also have a bad IAC ( idle air control) but try eliminating any vacuum leaks and cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.