I would guess, that idle should be around 600 rpms on an engine that is at normal operating temp, with no load(A/C not on).....
Recommended spark plug replacement is 100K, but that is not written in stone....I assume this vehicle has already had a complete tuneup?
Last time your fuel filter was replaced?
Clean throttle plate and bore, along with IAC pintle and passage?
Checked for codes?