eBay's "Performance Tuning Chip" 100HP Gain, Gas Saver etc - A Legal Scam. Why pay at least $20 for a $.02 resistor in a box with nice sticker?!?  "Designed By the Skilled Engineers" Turns out it's just a $.02 resistor that replaces the air temperature sensor under the hood of your car. In reality it's not a chip, it will not add up to 100hp, and it's not worth the more than a quarter since the resistor is available at your local Radio Shack store (a 1000K resistor). It will actually not add any noticeable horsepower at all after EEC "adjusts" to the fake temperature. Basically, these "fake" chips are mostly a resistor that plugs into the intake air temperature connector in an attempt to fool the engine management computer (ECU) into thinking the intake air is somewhere around 32F and therefore changes the computer settings...in turn adding more power...they claim up to 100 hp. In sum, it will potentially harm your engine because it "lies" to your ECU in a way that upsets oxygen fuel ratio.  What it does is trick your ECU into thinking the air coming into the engine is cooler than it really is so the ECU will advance the timing more and increase the amount of fuel going to the injectors. You would almost surely need to run premium fuel so you don't get premature ignition of the fuel-air mixture, and your fuel mileage might suffer on top of that. Fact of the matter is you can get the same result by just advancing your base timing setting a couple degrees, but you'll still probably need premium fuel.  It is a true reprogramming of your factory ECU and is customizable based on your other modifications. It costs $400, so I would only do it if you have other mods. The gains seen without other mods probably wouldn't be worth the cost, but with mods it would probably have a noticeable, though not huge, impact on performance. You get what you pay for and horse power isn't cheap, in addition your check engine light might come on, that would be the only difference you would notice. eBay doesn't get involved in validating the legitimacy of products.