A mate is having problems with his Tigra 1.4XE,it's an M reg car. he says it gets spluttery when driving hard-ish, he took it to a garage and they did a fault find on it,and it said the knock sensor was faulty,now the man in the garage said he'd never seen a knock sensor go down,so it was more likely the ECU,the bill would be £260 for a replacement unit and unlocking by vauxhall (he said they are immobilised???)

so,where is the knock sensor on the engine,and is an ecu such a difficult job to swap,or could i just unplug and try a different unit,oh and where is the ECU too