engine wont idle at all after lower intake gasket replacement

attemped to replace the lower intake manifolds on my car. after completion i started it and it would not idle whatsoever. it would only run if i floored it and then it would run all the way to the limiter and as soon as i let off it would sputter and backfire through intake and die. i have checked plug wires, electrical connections, fuel injectors for proper seating, and i have even now takin it all back aprt to check the pushrods and they were all right. i did manage to brak a few plastic lines when in was dissasembling. one of these is the line that comes of of the small box located behind the coil pack. i also broke the one coming out of the front valve cover and top of throttle body. but i doubt these would make it run so poorly. like i said it would not idle at all just die. and at half throttle it could barely maintain rpm and was sputtering and backfiring through intake. now that i have it all aprt again i just dont know what to do.

attemped to replace the lower intake manifolds on my car. after completion i started it and it would not idle whatsoever. it would only run if i floored it and then it would run all the way to the limiter and as soon as i let off it would sputter and backfire through intake and die. i have checked plug wires, electrical connections, fuel injectors for proper seating, and i have even now takin it all back aprt to check the pushrods and they were all right. i did manage to brak a few plastic lines when in was dissasembling. one of these is the line that comes of of the small box located behind the coil pack. i also broke the one coming out of the front valve cover and top of throttle body. but i doubt these would make it run so poorly. like i said it would not idle at all just die. and at half throttle it could barely maintain rpm and was sputtering and backfiring through intake. now that i have it all aprt again i just dont know what to do.
I have the '98 Monte with the 3.1. If I unplug the plastic vacuum line on the front valve cover at the PCV valve, my car would be extremely difficult to keep running. Same for the one on the back that you've described. These are major vaccum lines and if they leak, you will have trouble like you are describing.

gdipilato, rkvons is right, sounds like you have some vacuum leaks to fix.