as somebody has already said, all they do is trick your ecu into thinking that the engine is running cold. most of them modify the read out from the lambda sensor (on the exhaust). but beware, they will give you long term engine problems. everyone should know that petrols have to have a very curial balance between fuel and air. run too lean and you risk over heating the pistons and melting them; run to rich and the petrol dissolves the oil lining the cylindors leaving you cylindor walls and pistons un-lubricated hence leading to excessive wear. they are a very crude way on gaining false power.
the only simple ways to gain true power and torque come from modifying the induction and exhaust system, remapping the ecu properly and of course doing regular servicing.
any of those people still wanting to do it, the resistors i should think will come with fitting instructions
