vacuum leak
 

what does it feel like? i am having random RPM surges and i believe it is a MAP sensor vacuum leak.

spray some throttle body cleaner around the area where you think there is a leak. if the idle smoothes out, you found your leak. if the idle doesnt smooth out, you probably just need to get the car tuned.

I think he has an LS1, MAP sensor is tough to get to. Could be a vacuum leak, most common ones are in the T/B area. Does it happen all the time? Just when it is hot? Just on start-up? Also your car will idle very poorly with a vacuum leak. mine would stall alot cold when I had a leak. Is your RPM surge at idle or when you are driving? Do you have a stick or an auto?

its a manual with a mail order tune. i don't think the RPMs would surge as drastically as they do from a tune. they can sometime fly as high as 4k+ or down to the point of stalling, which it does at times on cold starts. this is not a once in a while thing either, it happens constantly. another reason i want to rule out the tune is because once it eventually finds idle, it idles damn well.

my first thought was the throttle body. so for safe measure, i replaced the TPS. no dice. popped the hood, motor was at ~3k, but throttle body was closed. car cannot rev without air right? wouldn't that constitute a vacuum leak?

definitely sounds like a vac leak, my gp did the same thing the one time i left the pcv line off the TB

Check your PCV and fresh air line, if you can reach the MAP see if it is nice and tight. Did you check the gasket betweenthe TB and manifold? Rare but they can get cracked, especially if you had the TB off. Also check the line off the back of the manifold on the passenger side that runs to the HVAC.

checked that one, its good as far as i can tell
i have no idea what that is. wheres it located?
thats what i think it may be. i'll check it when i get to my car.
i think the leak is too big to be a bad seal between the TB and the manifold if it is allowing the car to rev so high
i have no idea what that is either, i'll check for it though

if the gasket cracked and either fell out or got sucked into the intake...there is potential for a big enough leak. mine would rev up to 3k with the pcv hose off...iirc it was only a 5/16" line