noob needs help with mileage - only 10 MPG!

slantsixdan, rmchrgr,

Thanks again for all your replies and all the info.

It was about four weeks ago when I picked up the car and spoke to the mechanic, so I may not have remembered exactly what he said about that knock-like sound that occurs only at idle when the engine warms up.
I don't want to bad-mouth the mechanic on this forum.
I'll get in touch with him and ask about valve adjustment.