As I work my way through two HT4100-equipped cars (and one 4.9-engined vehicle), I have a few more tips for everyone out there:
1. Make sure your heat stove pipe is properly connected to the air cleaner and also the exhaust manifold heat shield (this is only for owners of TBI cars). These sometimes come unconnected/break after the air cleaner gets removed a few times since they're somewhat fragile. While it may seem like you always want cold air flowing through the air cleaner once the engine is warm, the HT4100 is calibrated to run with an intake air temperature of 131 degrees Fahrenheit. Also, check for proper operation of the ThermAC damper door. Make sure it closes when the engine is cold, and opens once the interal air cleaner temperature rises above 131 degrees.
Now that winter has arrived in many states, the heat stove operation is crucial to optimum performance and economy in our vehicles. One of my cars had a slight hesitation when I first depressed the gas pedal. I finally traced it to an unconnected heat stove. Now the hesitation is gone. If you don't believe me that this can be the cause, simply look in your factory service manual under "hesitation" symptoms. I didn't believe it myself.
If you don't have the heat stove on your car (or a loose one), here's what happens: as your car idles, the intake air temperature will rise simply because the engine is hot, and not much air is flowing through the manifold. The IAT sensor will then tell the ECM that the air temperature is rather hot. Then, when you step on the gas to accelerate, very cold air suddenly enters the manifold (as it is sucked in by the engine vacuum). This shocks the IAT sensor, which takes about .5 second to respond to the cold air. Since it was previously telling the ECM that the intake air temperature was hot, this mixture is too lean for the engine, causing a hesitation, until the IAT registers that the intake air temperature is cold, and the ECM adjusts accordingly by richening the mixture.
2. If you haven't advanced your timing to about 12 degrees base (from 10 degrees), do so. If you have a TBI 4.1 or 4.5, simply run mid-grade. You'll experience what feels like a significant power boost, and your gas mileage will also increase. I drive the same route everyday at about 65 mph (about 90% freeway). Before advancing the timing on my new vehicle I got about 22-23 mpg. Now I'm consistently getting 26-27! I'll pay the 10 cents/gallon increase (about 3% larger fuel cost) for a 10+% economy boost and more power.