Hello, here is an report for this car. The injectors have been away for testing and cleaning, they where very dirty. After I fitted them back in I thought the problem was still there, so I posted this on autonerdz forum also, and I found some people there who gave the same advice as here, also found that Robski was there also so became the same advice from him there also. Won't do that again posting in 2 forums. But to keep a long story short I started the car yesterday cold and the problem seemed to be gone, also drove the car and the fuel trims where much better as the first I posted here. Started the car again this morning and the backfire and hesitation when you hit the throttle is gone, there is still a slight misfire when it runs, so my thoughts are that the coil pack indeed may have an problem as suggested here, but because the shop before me tried the coil pack with the dirty injectors they didn't notice any difference. Will try to convince them to put on a new coil pack.
Thanks for the advice given here to me, and I hope I may post again if I got a problem car back in.