I haven't ran the numbers yet but my fuel mileage seems to have gone down since I cleaned up my engine bay. Here is what I did.

1. Removed A.I.R. tubes from exhaust manifold and plugged the holes.
2. Removed all the tubing that went from the A.I.R. tubes to the black box and the black box.
3. Removed the Smog pump.
4. Removed the A/C compreser, the A/C condenser, and all the tubing in between.

Should this, in any way, lead to a bad fuel mileage? Thanks for any info.

 

If you are talking about the tube that runs from the engine to the black box that is on the carburetor then yes. I removed that tube and not only did mileage suffer but engine overheated. It turns out that the carburetor actually sucks the hot air from the engine to be burned with the gas.

 

Why are you removing all this in the first place? None if it is hindering performance, all your doing is further reducing the value of the car. Make sure you get rid of the catalytic converter if your getting rid of the AIR system, since the AIR keeps the cat functioning properly.

 

Because I don't need any of it and a clean, uncluttered engine bay is a beautiful and worth-while thing.

Weight hinders performance. But performance isn't why I removed it all.

A. My car is not for sale and never will be. B. On what planet does having a perfect engine bay reduce value?

Already done.

But yea, the fuel millage issue turned out to be a crappy sender. My gauge was all over the place, heh. Luckily the previous owner cut 3 corners of a square above the fuel pump!

 

The only emissions gizmo that will affect your fuel mileage is the EGR as mentioned by the first reply. Exhaust gas recirculation at cruise speed can give you 1-2 MPG on the highway.
PCV keeps your rings sealed better and keeps your engine crankcase cleaner, but I don't think it necessarily improves mileage.