Hot air intake, sounds like watching C-SPAN when Congress is in session.
I'm aware of the following:
- Ebay resistor scam - from time to time, you'll see someone advertise a $0.05 resistor that for $20 or more improves fuel economy "xxx%". These typically shunt the manifold temperature sensor so the car thinks the air is warmer than it really is and 'fool' the control computers. This is a fuelish decision and has been widely debunked . . . still, a resistor customer is born every minute.
- Honda Insight Lean-Burn - my understanding is some of the original, lean-burn Honda Insights achieved mileage improvements by having a duct bring heated air from around the exhaust manifold and pipes. I suspect it was from getting the engine to run in 'lean burn' more frequently but am not sure.
- Good Prius Friend Hobbit experiment - tried it but his reports were that any effect was beyond his ability to detect.
- Some Prius idle effect, maybe - in my oil additive testing, I noticed the initial fuel consumption was quite low at idle after running at highway speeds and parking but after a few minutes, I could see the spark retard and fuel consumption increase. This MAY be due to the intake manifold cooling off and thus cooler air. However, I have not yet studied this effect. Given the Prius normally turns the engine off rather than idle with the engine running, it may be moot.
Do you have any engine instrumentation that includes: spark advance, coolant temperature, MAF and intake air temperature?
Bob Wilson