MAF P0100 code 1.8 TSI

I have the engine light on and a P0100 Maf code.  The engine starts and runs fine no jerks or stuttering when plugged in or disconnected.  The Maf looks clean, is it worth spraying on a petrol engine ( well maintained )    I am getting a constant flow reading of 684. 06gms/ sec.  ( plugged on or not)         Having looked @ the plug I get ( ignition on) no.1  4.9v temp signal?   no’ 2 ground    no. 3- 12mv    no’4 11v     no’5.  3.12 volts     Is the Maf duff or is it the main feed, no3? not doing it’s thing ( should be 12v?)  any suggestions welcome