I'm going to assume (usually a bad idea) that you understand the basic theory about how and why the Warm Air Intake works and some understanding about automatic transmissions, more importaintly, the Torque Converter oeprations.
In an effort to get at LEAST 30mpg highway without having to P&G in my tracker I decided to give the WAI a try. I've changed my acceleration to hard ont he gas hovering around 4500 to a shift until I hit 35mph where the TCC locks itself and then continue at a steady speed(in town of course). I removed the tube from my air box that was there to pull fresh air as opposed to the surrounding engine bay air and gave it a whirl.
The engine was noticeably louder under load. If the engine was in a small RWD 5 speed car I would have loved the sound, it was simply incredible, but for a small SUV like this it was nothing but annoying, especially on the freeway where the engine ends up being under heavy load to keep 75 and really sucks on a long trip.
I can honestly say I didn't like it after the engine warmed up. When the engine hadn't fully heated up and the engine bay was still cold it ran like a top but after the radiator and engine both warmed up I ended up with an even bigger dog of a car than I already had. This wasn't too big of an issue I guess seeing as that is how the WAI is supposed to work.
I had gotten an all time freeway high of ~26.5 mpg and even that I only got once, usually it hovers around 23-24mpg @ 75mph (VERY lame). With the WAI I averaged a trip total of 24.3 mpg. Not very outstanding. Since so many people on here rave about the WAI increasing mileage by 6% or even more I started to wonder just what was going on.
Of all of the different things out there that could be options as to why it didn't work like: ECU in a limp mode, ECU doesn't read very hot intake temps well, O2 sensor bad, or even the air wasn't hot enough, I ended up not blaming it on the engine. This is what lead me to my torque converter lock-up mod. I can manually lock the TC any time the transmission is NOT in first gear.
The confirmation of this came this morning when I was on the freeway to work and found myself at around 90mph(don't ask) and, to my astonishment, I was able to look down at the dash and see my green 'torque converter locked' indicator light glowing. It was 51 degrees outside and the engine was running GREAT.
Then I started thinking to myself, "you know, on a hot summer day I can barely keep 70 while pressing the gas little enough to keep that converter locked and here I am doing 90 and it's locked no problem". I pressed the gas down more until it unlocked and I'd say I had a good 15-20 degrees of throttle left before it unlocked.
Basically, the reason the WAI didn't work for me is actually the same reason that it's supposed to work for everyone else. Opening the throttle more to get the same amount of power(reducing pumping losses) ends up putting my throttle position to a point that the converter never locks on the freeway, totally negating any benefit the WAI may have possibly had.
Now that I have my manual TC override I need to take another trip. My only issue, again, is noise from the intake being rather annoying on the freeway. I also have my $20 craptop so I can start datalogging on more than my single channel TI-84+
located in the bottom left corner of the post. 
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