Keeping the board going with more questions! :)

So...quite a few years ago, I removed the corrugated pre_heated air hose from my car, removed the thermostat from the air box, then plugged that hole with the cap from a jar, that just happened to fit.

I recovered this car last year (I had sold it when going back overseas but was able to buy it back), I realized that cap was missing. Just this past weekend, I plugged the hole again, using foil tape.

In this last tank of gas, since I've been monitoring my fuel mileage, it seems that the mileage has gone from about 19.5 mpg to about 18.3 mpg. I did change my plug wires recently, but that was 2 weeks ago.

About the only thing of significance I've done since the latest fill-up is plugging that hole. That and slightly tightening the accelerator cable, that was a bit slack. I gained some response as a result but I doubt that it would be a culprit in the gas mileage.

So, as I was plugging that hole, I was thinking, what if I'm actually restricting the air flow, and in the case of a properly functioning thermostat, we would have actually both air pipes open.

Does that make sense, and should that hole actually remain unplugged against the "conventional wisdom"? Could this be reflected in this loss of fuel mileage over a fill up (all previous fill ups over the past several weeks have clocked at 19.5 pretty constantly). Or, should it remain open and be redirected to get air from in front of the radiator instead, like the other air intake?

I'll probably try to open it up again and see what numbers I get but I wanted to throw the question out there.

I should add, this is Arizona, and it's hot outside.