Yeah, I know the thread's old, but I'm looking for something and this is interesting. Magnuman's Post is the closest to real operation.Under cruise conditions the Manifold Air Pressure sensor (MAP) acts like a barometer, and sends this info. to the Power Control Module (PCM), which in turn adjusts injector pulse width to maintain the 14.7:1 air-fuel mixture. This is the main input that controls mixture at different altitudes. The Intake Air Temperature sensor (IAT) provides input for changes in temperature. It's really a pretty complex, yet neat setup, but would be better if it were a Mass Air system. The limits of our Speed Density system are mainly the pre-programmed limits/ranges of the PCM. These limits/ranges are designed to accomodate nearly all environmental conditions we are likely to encounter. To indicate the complexity at cruise, for instance...the PCM adjusts mixture by using inputs from MAP sensor, RPM sensor, IAT sensor, engine coolant temperature, camshaft position, knock sensor, throttle position, 02 sensors, air conditioning switch position, battery voltage, and vehicle speed. At Wide Open Throttle (WOT) inputs used ar IAT sensor, engine coolant temp., RPM, knock sensor, MAP sensor, and throttle position. The fuel injection system also has built in pre-programmed short and long term fuel correction (adaptive memory) routines that are triggered anytime mixture reaches a predetermined "switch" point. The adaptive memory is a whole different bucket of worms though. My head hurts! Guess we've pretty much beat this to death.
With regard to Cold Air Intakes (CAI's), the main approach I used is that the cooler air (denser) in, the better for performance and gas mileage. Really though, at this point I am more interested in the gas mileage. This is why my home built CAI utilizes an additional air inlet from behind the grill to the airbox (in addition to the stock "eardrum" inlet in the fenderwell), a double insulated stock airbox, a K and N drop-in filter, and a double wall, double insulated intake tube from filter to plenum. I don't know if this, by itself, works, but I do know that with this and my other minor mods., my in-town and highway mileage has increased significantly. I now get 15-18.4 mpg in town/rural, and 27.5-28.3 mpg on the highway between 60-70 mph. I have recently changed to synthetic oil and will be taking 600 plus mile trip next week. It will include mountain, flat land, and rolling hills. I hope to do even better now. For those who doubt, a true COLD AIR kit...not drawing heated underhood air is a good investment IMO. If anyone is interested on how I did mine, I'll start another thread that specifically addresses my CAI. Let me know.
Two things to consider at WOT.
1) The long term adaptive memory does impact fuel/air mixture settings. As quoted from the service manual:
"The values stored in long term adaptive memory are used for all operating conditions, including open loop and cold starting"
2) During WOT "The PCM adjusts injector pulse width to supply a predetermined amount of additional fuel, based on MAP and RPM."
I'm searching for people experimenting with changing the sensor value for the IAT sensor to adjust the fuel/air ratio. However, this needs to be done only at WOT or you impact the long term adaptive memory and could negatively impact closed loop modes. (The O2 sensor readings may compensate for this, however....)