had a new exhaust ,turbo back system, i have put old lamba sensor bak in but could this be knackered, it only hesitates wen engine is warm, took it to a performance place and they said lamba sensor would be doing this !!!!!

 

Does it happen when on full boost? The lambda signal is not used when your at WOT on boost. If the hesitation still happens then, then it's something else causing the problem.