I've been chasing vacuum leaks for awhile in an effort to improve the LTFT (long-term fuel trims) on my'05 Sport sedan with 154,000 miles. I've replaced every hose leading to the intake manifold, the PCV valve as well as IAT and VVT seals and O-rings. With all of that the trims waivered around 10% and 7% (Banks 1 and 2 respectively). It turned out that the VVT seals appeared to still be leaking slightly so I gooped them up with red RTV and the trims dropped to 4.7% and 2.34% which are probably as good as I'm going to get. On a whim, I installed a K & N filter I'd foolishly purchased thinking it might improve performance (for sale cheap if anyone wants it), drove the car for about a half hour and rechecked the trims, which had now climbed to 11.7% and 7.03%. Re-installed the stock filter and they dropped back to where they were before. There was no discernable difference in performance between filters, although I'm sure that the lower fuel trims with the stock filter probably/hopefully had a positive effect.