Gas mileage and RF noise Improvement all in one fix!
I recently heard lots of buzzing in time with engine speed (especially when using the radio tuner iPod adaptor, and noticed gas mileage was down to about 26 MPG. I usually average about 29-32 (this is a 94 2.3L 4-cyl, 5-speed) so I knew something was up. I changed the plug wires and all is well. My hypothesis is that the spark was grounding out to the block on occasion causing the radio frequency noise. I was back to about 29 MPG last time I checked. The #3 cylinder plug under the intake manifold is difficult to access but using a long set of needlenose pliers with a curved end allowed me to reach right through the opening between the intake manifold branches and pull the cap. The right tool for the job makes it much easier than removing the whole manifold. Another recommendation is to disconnect and replace only one lead at a time (especially on the twin plug engines) so you get the right firing order. It's easier to match lengths that way too.
Hope this helps someone!