2000 Honda Passport vacuum leak rear of engine

I have a vacuum leak at the rear of the engine, it is so bad that the truck won't idle and pops back through the intake when rpms are run up, I replaced the small line to the evap solinod but still have a leak. I can't see any other lines, but when I spray silicon at the rear of the manifold the engine revs up and runs good. Is ther another line back there? do I have to remove the penlum to get to it? Could it be the throttle shaft? any help would be great!
p.s 8in vacuum at idle
Brian