[catvents]

One point mentioned by Wiswind is a vacuum leak and according to your post, condition seem to be worst when you apply the brake which use (if I could say) a big amount of vac to operate the booster. If not already done I would take a serious look at the few vac hoses between the engine and the firewall, in addition to the brake booster, there is another big one connected to the base of the intake plenum on the passenger side and also a few little which feed the Vapor Canister Purge Valve and the EGR Vacuum Solenoid (on the firewall). Just a few idea if not already done.