Hi everyone i'm new here with a 95 blazer. I recently bought this car and found this problem but was not able to figure out what is the cause.

Everytime i start up the car it will rev up to 3000rpm and stay there, when driving you won't notice this but at a stop the gauge will stay at 3k rpm for a good 1/2 hour or so before dropping down to normal. Any idea???

 

Large vacuum leak or bad IAC (idle air control) valve.