my 91 Chevy 5.7 throttle it body has developed a surging I'm not sure what's going on I start it and it will run from 600 to maybe 2000 rpm just up and down. I haven't looked at it yet I just took a different ride to store. It acts like a vacuum leak, but that would stay all the time. You can rev it up and it runs but at idle its all over the place. Any ideas before I start this venture?