Hey jon your prob is not the air flow but the camshaft sensor depending on the engine you have remove the timing belt cover and you should see by the cam sprockets the sensor sitting to either the left or right side nine time out of ten you can usually take it out re position it and connect it back up to the system and disconnect the battery (black only) for 15 mins and bobs your uncle failing that new sensor as for speedo on rear drums should find two sensors just above the handbrake lever and beside the mounting bolts check the conections
vauxhall vectra guy
May 2008