My car is Reving in Neutral on its own.?

-i have a 2000 mazda b2500 2.5L 4 cly, 5speed. For some reason when i shift from any gear into Neutral the car begins to rev at high rpms and doesn't stop unless i turn off the car or come to a complete stop. Any idea what could be the problem? This happens ever once awhile. But sometimes happens often.Remove the big intake hose, can of choke cleaner and a tooth brush, go to town.. clean, scrub, open throttle body flap (butterfly) and clean, spray. Wont hurt anything, 1st crank blows it all out. Now, if it returns then you maybe looking at a TPS or IAC valve (throttle position sensor or idle air control valve), those may store a code that any parts store can read for free. Clean 1st.sounds like the idle air control valve is getting bad.if your check engine light is on you can take it to auto zone and they can scan the code for ya free of charge. Hope this helps ya.