Blowby from the passenger side PCV circuit is where this generally occurs. Fixes run from cheap & simple to expensive & complex. You'll need to thoroughly clean the TB and IAC valve. Double check the stock elbow & hose. Any (vacuum) leaks create unmetered air conditions which can, in turn, decrease efficiency/mpg.I was look at my throttle body and I notice I have oil in it. There was a little bit where the intake connects to throttle body. What does this mean?