It will allow you to program the ECU in your car to your liking. You can adjust the speedometer readings for gear ration and/or tire size changes. You can also adjust the ignition timing to your liking, and if you know what you're doing, you can adjust the fuel pressure to make more power, but unless if you know what you're doing, I wouldn't fool with that. You can also do things like adjust fan timing so that fan will come on sooner, which is what most do when running a cooler thermostat. You should be able to buy a hand held programmer, like the Predator or SCT unit for under 400 dollars.BigChiefSmokem said:
As for the CAI, it all depends on what kind you're getting. I don't know much about the JLT cold air kit, but you would probably be best by getting a CAI kit that is made of plastic, and doesn't have a bend in front of the MAF meter. I have the K&N FIPK and I like it.