"Resistor in a box", performance chip, etc, call it what you will it's a scam. It's not something to concern yourself with on your car: the theory here is that the air temp sensor (which we 240 drivers don't have, except as a function of the air mass meter) gives a resistance value that varies depending on temperature (a simple thermisistor). Find out what resistance value applies to cold air, ie 32F, for a given sensor, because at that ambient temp the engine will bump up timing a bit because of the lower potential for pre-ignition (cooler air=better performance). That's the theory. So by unhooking the temp sensor & replacing it with a fixed impedance resistor the ECU applies the engine management program for 32F and you gain power because the timing's bumped up(THEORETICALLY!). However I do not expect theory translates into practice here - there are also issues of mixture (& the relative density of fuel at different temps) to consider. And the knock sensor would be bumping the timing back down, and dumping fuel to lower combustion chamber temps (loss of power, in effect). Certainly not something I'd do to any car of mine, even if it was applicable to my vehicle. In a nutshell, just smile & nod & be glad you weren't the guy who paid $75 for a $0.10 component that defeats the engineering of your engine management system...
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf