30 DOLLAR E-BAY Performance chips?
#4
First. You just answered your own question here.
Second. Even if they did work, on the HHR the computer's "learn down" feature would cover up any changes within a short period of time.
Third. Most, if not all of these "gimmick chips" are nothing more than a diode or a resistor inside a "tech" looking plastic cover. (High tech ones may be both a diode AND a resistor..... Ooooh! fancy) Hardly an actual "chip".
Fourth. If there were MPG and Horsepower gains to be had by such a simple means, wouldn't GM have instituted this themselves?
Just my 2cents.