BMW reving by itself

Hey Scotty!I saw a BMW getting in higher rps by itself

One day i was going to school and saw a bmw sitting in one place (parked but running) and the owner outside angry because the car was reving like crazy by itself.I was wondering what could cause that and asked my teacher in school (i learning about cars) and she couldnt answear me , so i was hoping you can! (sorry for bad english,and on the pic is just the model e36)

often vacuum leaks do that on Beemers, cheap plastic parts crack with age, then suck air

early 2000s BMW's are the last reliable cars that BMW made past 2006 nothing was at least a little bit reliable anymore. the most reliable BMW's are the 70's,80's and early 90's. My E53 BMW has 200,000k miles on it and it runs great but you need to replace the plastic cooling parts every 95k miles.400$ each 95k miles. I haven't had vacuum leaks though but I usually don't mess with the rubber and plastic over in that area.The engines are bulletproof but everything that keeps that engine cold usually goes bad and that's what ends those engines.