1996 4Runner 3.4 V6

Crank and turn over are the same thing. If you hear a single, kind of loud clunk from the starter each time you turn the ignition switch to "crank", but it doesn't spin the engine, suspect worn solenoid contacts inside the starter solenoid. This is real common with the little silver Nippendenso starters. Those contacts can be replaced for 20 bucks, but most people just replace the entire starter.

This problem always starts out being intermittent and it will crank eventually if you cycle the ignition switch from "run" to "crank" enough times. It will get progressively worse over time.