alright i have an 89 iroc 305 tpi 5 speed standerd and for what ever reson when i start it up its fine for maybe 30 secs and then the rpms will shoot up to 2500 for about 10 secs and then it will slowly go down to about 500 rpm and then it will pick back up to 2500 and it will continue to do this untill i shut it off and i am not touching anything and i have not done anthing under the hood for a long time and it just started doing this a few days ago any ideas would be a big help thank you