I have a hesitation off idle and backfiring through the intake. I checked the timing and it is set at 11 degrees, but when I rev the engine at wot off idle, the timing will retard to 0 degrees or less, then advance back above 11+ degrees once the backfiring clears up. I checked the vacuum at the port on the throttle body, and i get 15 inhg when revving and 0 at idle. I pulled a vacuum line off the intake manifold and the car started to idle at 1,100 rpm, but it will rev like it's supposed to. It also caused the timing to retard to 0 degrees, but it advances when I rev it. The vapor canister and egr have been removed and the lines are capped off, but other than that, the vacuum lines are all in the original locations as far as I can tell. Any ideas what could be causing this?