Hmmm. I was leaving off the brake booster vacuum hose. Thats the little hose that attaches to the backside of the manifold. I should have counted and remembered there are 3 hoses connecting to the manifold.

I recently bought a 2008 vibe with 144K but was getting only 25mpg. I replaced the intake manifold gasket with the orange one from toyota but was still sensing leakeage on the far right end of the manifold and now getting a p0171 error. I've now permatexed around the gasket and I think the leakage i...