car turns on then off. happens periodically. i hit the start button, the car revs on and then slows and shuts off. why is this happening?

 

could be a dirty throttle body. any check engine lights?

 

This frequently occurs when the throttle bodies are filthy. Preform the following procedure (all the steps are easy to figure out via google, forum search, service manual)

-disconnect the negative battery terminal
-remove the throttle body, leaving it connected to the wiring harness. The front will look clean, the back will be disgusting.
-lay down a towel/old t shirts/whatever under the throttle body to catch runoff
-with the throttle sensor facing up to prevent soaking the electronics, hose down the inside with CRC throttle body cleaner and wipe with a rag. Use an old toothbrush on stubborn grime. Be very gentle when moving the throttle plate
-reinstall and repeat on the other side
-reconnect the battery
-perform the "accelerator pedal released position learning" procedure
-perform the "throttle valve closed position learning" procedure
-perform the "idle air volume learning" procedure

Repeat every 40k mi or so

 

Sounds more like a vacuum leak