Okay, I know the deal when it comes to this mod, I know how it's supposed to be used, performance-wise, but I must tell you, for our cars, this will not do a damn thing.
The resistor trick is old-school, and you have to do it right. Furthermore, it will not work on any ODB-2 vehicle. it usually
works on odb-1 and older electrical systems.
It works like this, you solder a resistor or a variable resistor (pot-type) and wire it in-line on one of the wires of your Intake
Air Temperature(IAT) sensor. Some people also use this trick on their Engine Coolant Temperature(ECT). Because there's resistance on the line, the ECU registers the temperature as colder than it actually is (because there is less voltage going to the ECU. on older cars, this alters timing, runs the car a bit richer, and can add a few ponies. Using a variable resistor allows one to "fine tune" the A/F ratio better, as well as adjust timing a bit.
I used to have this on my escort, I built a knob box with two variable resistor pots, and wired it into the ECT and IAT sensors, and it worked, to a degree...
The problem is that a car's ECU will eventually "tune out" the altered signal over time on ODB-I and II systems. You'd set the POTS to the resistance you need, start the car, and it'd get maybe an extra 5 HP or so on my setup (which included I/H/E, MSD ignition/9mm wires/iridium plugs, headwork, etc) However, after about an hour or two, the ECU would tune out my settings, and it'd perform normally, mind you, this car was ODB-1. On ODB-2, it won't last a minute before the ECU compensates on it's own. At Wide-Open throttle, this mod is useless, since the ecu is in closed loop, and doesn't read off the sensors at all, it goes off the ECU's programming alone, and is not affected by sensors.
This mod is only useful in part-throttle conditions, it will improve midrange and low a bit, but top end will not be affected.
Get a S-AFC, it does the same thing, but has more sensor hookups and is microprocessor controlled, same wiht the JET module and Venom 400. they work in a similar fashion, but are continually adjusted, so the ECU doesn't "Catch on" to the altered signals. They're also more tuneable, and can produce better gains. Resistor mods are too old-school to work on modern ODB computers. Now if your car is older, it may work, but not in any huge degree.
If you guys want, I can make an in-depth how to, showing how to select resistors, install them, and tune them (if potted). However, I don't think it'll do much for us. Better to go piggy back instead.