'03 GTP. 138kmi. Open cone air filter, 180* t-stat, res. delete, flowmaster 40s, otherwise drivetrain is stock. I used to pull 7+psi boost at will, and would peak at over 8psi regularly. Last several months its gotten gradually worse, to the point that I only get 6-6.5psi boost.. Also, I've gotten a couple P0440 codes. Fresh/clean fluids, air filter, pcv valve, autolite 606s. I've tried spraying carb cleaner around, a few times, with no affect. So couple easy questions, before I throw $ away on all new vacuum lines or a mechanic diagnosis. Before we start, let's pretend vacuum lines are not leaking. 1) what else could cause loss of vacuum/boost (and likely the P0440), eg plenum gasket? evap vent solenoid? evap purge solenoid? bad vapor canister? bad gas cap? bad fuel tank filler neck? BBV solenoid filter? I'm grasping, but it would be a huge help if I could eliminate some possible problems in my trouble shooting. 2) What is a good vacuum pressure for a warm idle, or in P, in inch/Hg?
Thanks a ton in advance.