Okay, some good news and some bad news:
First, the good news: I could do a run with the HAI turned off.
Route C Data Set (26.5 mile distance)| Label | Date/Time Stamp | Consumed | FE | Outside Temp | Intake Temp | HAI Status | %Change |
| B | 2012-05-16 1:40 AM | 1.40 gal | 18.93 MPG | 62 F | 104 F | Active |
| A | 2012-05-17 1:47 AM | 1.49 gal | 17.79 MPG | 42 F | 58 F | Off | -6.04% |
This B-A test set shows a decrease of 6.04% from B to A. (and apparently we can use table bbcodes... cool!)
Now, the bad news: The heater valve, used to control the intake heater, allows a little bit of hot engine coolant to the intake heater when the valve is switched off. The supply line was warm to the touch at the end of the test route, but the return line was cool. This caused the warmer-than-expected intake air temperature observed during this night's run. If pure results are desired (HAI turned absolutely off), then I might have to invest in some sort of globe valve to install in-line with the heater supply.