Carried out WOT test this evening in 3rd gear as suggested by Jamie. All measurements in volts only. Origninal MAF showing 3.2volts max. 2nd hand unit fluctuating wildly between 0.4 and 3.2 volts. Interestly I mentioned in an earlier thread that last 3 digits of original unit had been shaved off and no match with 2nd hand unit could be made. This was not so. Further investigation showed it was the s/h unit that had been tampered with. Draw your own conclusions. Customer politely advised to obtain a Bosch or Vauxhall unit. He will report back with results and will let you know. Many thanks for your interest and inputs. Pete