If you do a careful test there will be no MPG difference on a fuel injected, o2 sensor controlled, gasoline engine due to air filter restriction at part throttle. Even highly “clogged” dirty air filters have no measurable MPG effect on FI/ O2 sensor gasoline engines at part throttle.
Heated intake air at part throttle operation “slightly” improves fuel economy, unless the PCM starts retarding ignition timing a lot when it senses hotter intake air via the IAT sensor. Both OBD-I and OBD-II Magnum V8s retard ignition timing as either IAT or coolant sensor shows hotter.

This is not true of carburetor gasoline engines. In those older carb engines air filter restriction affects the air to fuel ratio.

This is not true of diesel engines. Low restriction air filters on diesels raise the air/ fuel ratio. Low restriction exhaust systems also raise the air/fuel ratio on diesels.