Mazda 3 2005 automatic rpm high in neutral how to fix

The problem started when I had a mechanic clean my car's throttle body (it's a 2011 model with 90,000 km; I haven't driven it much). Since then, it has had idling issues. The engine suddenly revs up to 1,500 rpm and then drops back down. I’ve visited several mechanics; one suggested the neutral switch was the culprit (which makes sense, as pressing the clutch when it revs causes the acceleration to stop and the RPMs to return to normal levels). Another mechanic ran various tests on the throttle body—including a smoke test to check for leaks—and while the frequency has decreased, the issue still occurs about 10 times during a half-hour drive. What can I do? Thanks.