Pontiac Repair: 04 Montana miss fire, intake manifold gasket, vacuum leak

Question
Hi, I have an 04 Montana Van and its got a miss fire on cylinder # 5. I've changed wires and plugs, tested the coil. everything checks out, I've also tested injectors but all seem to be fine? any further Ideas? Its an intermittent miss as soon as you take the RPM's up it levels itself out, Thanks for all your help.

Answer
hey Ian:

how did you "Test" the injetor? have you done a compression test on this? how about a running compression test. does #5 show lower then the rest? You could have a lean misfire due to a lean injetor or a leaking intake manifold gasket. Any codes set on this other then a P0300? those are a few things to check . you can check for a vacuum leak my pulling the breather hose out of the hose between the throttle body and air claner and pull off the PCV hose an plug it then spary car cleaner into the valve covers and see uif the engine idle smoothes out if so you have a vacuum leak.
good luck :)