2001 Vauxhall Corsa car is hunting whilst driving in 1st and 2nd gear

Hi ive had my 51 plate corsa for a year and a half and has been running fine its had the timing chain and new fan belt fitted january this year at 81000 miles its at 86000 now and was running fine up until a couple of days ago just after the oil temp switch getting replaced because it was leaking (been changed 3 times now tho dont think this is the cause of the problem) i went to drive it and seemed normal until the engine het up just b4 80 on th temp gauge then the car started to shudder and reving itself and i had to nurse it home stayin at 15 mph and in second gear i managed to get it to the garage in the morning when the engine was still cold bt once it het up and started doing it again. The mechanic put his machine on it and it said there was a fault with the egr valve and the air flow meter both have been replaced now with new 1s along with a new coil pack, spark plugs and fuel filter as well as the throttle body been removed and cleaned seems to be running aliitle bit better bt still hunting in first and second gear but its allowing u to drive through it till 3rd and 4th gear the mechanics are baffled by it as its still coming up on th fault reader as the egr valve and air flow meter but both have been replaced with the same kind so dont have a clue wot else to get checked would be greatfull for any ideas thanks in advance