I have 1999 A6 1.8 standard gearbox , car starts ok but 5 -10 minutes into journey car cuts out (feels like it is immobilised for 20 minutes) then starts again and drives for rest of journey (eg 30 to 4hours) Same problem in evening Then when I leave work cars starts ok but but 5 -10 minutes into journey car cuts out again

Only symptom that has appeared on car Airbag like kicked on six weeks ago

Car 10 weeks ago feels to have more low end torque/power in 1st and 2Nd gear than it ever had from start.
Any body have any clue before i get the error codes ?