Oh God...

[captaincheez]

I've got a 1996 Jimmy, vin code W(pretty sure). It's got like 156,000 miles or so, got it from my former girlfriend who took decent care of it. I've been slowly doing tuneups and minor repair things, just to get it a little happier. So anyway, I'm driving home from work, and pull over for some random reason. I guess I was really tired or something, since after I shut off the engine i quickly turned the ignition back to 'on'. The engine kinda sputters a bit, but i shut it right off since i realized how much of an idiot i am. Don't think much more of it until I try to start it up again. The thing makes a popping sound, like something snapped, and then revved up to about 2500-3000 rpms, spews a fairly large cloud of smoke out of the engine compartment(smelled like burning oil, kinda), and then drops below idle and starts to stall. I shut off the engine at this point, yell obscenities, and give it another shot. Same deal, revvs up real high on startup and drops back down and stalls. If it doesn't stall right away it revvs back up again. No more oily smell or any sort of leak is evident... I have no idea what this could be. I'm going to go out later and do some tests on the thing and see if i can find out any more. Thinking a compression test would be in order to see if I popped a valve or something. Any ideas on what it could be?

P.S. It'll have to be moved by tomorrow, would it be a good idea to try and drive it? It'll need to go about half a mile, but I don't want to risk any further damage.

[AJT1961]

When it "popped" you may have blown out the round vacuum fitting on the top of your intake manifold (follow the PCV valve hose to this fitting). If that's it, all you have to do is reinsert it and lock it in place by turning it to the lock position. If not, carefully check all of the other vacuum lines and fittings, because the wildly loping idle you describe is how the engine behaves when it is sucking a large amount of air from a major vacuum leak.