2001 Holden Barina Barina XC 2001 No Guts starting up hill

I purchased a second hand Barina XC 2001 manual from a dealer. I needed to put my foot down on the accellerator when going up hills but after a hill start where the car stalled the engine light came on. I took the car back to the dealer and they "repaired it" saying the engine sensor needed adjusting due to the car being detailed. The car still had the same problem so I took it back to the dealer who said he had his mechanic look at it and had been driving the car and did not have a problem he "apologised". and assured me the problem would be fixed. It would be reassuring if I knew what the problem was so if he hasn't "fixed" the problem I can challenge it with why didn't your mechanic check the ..........