was just wondering, have seen these things on ebay and the like, and wondered what the story is... They appear to be a resistor that messes with the ait temp signal to the ecu and therefore 'gives you more power'...! Is this a pile of crap or does it actually work? Or does it have some evil side effects...?

eBay.co.uk: +20 BHP MOD - SKODA FABIA, FELICIA, OCTAVIA, RS + (item 120067704041 end time 30-Dec-06 20:30:00 GMT)

They fool the engine into over fuelling. May work for a while but you will generate fault codes onto the ecu and cause the engine to run rich. The claims are rather exagerated especially for a non turbo engine. Expect 1-2BHP extra.

Expect nothing extra, expect less: the engine management is (now) closed loop when warmed up. It wasn't on some of the first American cars to be crippled in the name of emissions, and that's where this fudge originated.

If all the sensors on your car provide the correct values it will run at its best for a given ECU mapping. If one sensor is wrong (because you're trying to fake air temperature value, for instance) it will probably go into "limp home" mode.

Your mileage may vary.

i used to have a similar one,it gave a bit more torque at low revs,accelerated a bit faster,but the warning light came on the dash,and it's not woth it if you have to keep going back to the dealer to get the ecu reset. Having done more miles now ,my engine is much more reponsive and goes better