Pontiac Problems? Ask a Mechanic for Answers ASAP
In that case I'd suggest to 1st remove the intake and ensure that the throttle blade is clean and free from dirt that would prevent it from fully closing
and the best method for checking for a vacuum leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
its also worth disconnecting the brake servo hose and plugging it on the engine side
as I've known brake servo's to leak and allow air into the engine that way