Just had a De cat down pipe put on my car and it's running really lumpy like it's miss fireing or fuels not getting threw. When I accelerate the revs go up then it will judder as if it's getting held back or its struggling but after a few seconds it gets threw it. If anyone else has had this and nows a cure pls pass it on. At a guess could it be the lamber sensor on the decat it needs tweaking of such so the mixture is better ? that's purely a guess it is annoying

 

I'd guess you need a re- map mate. Careful you don't blow it up with boost spikes and incorrect fuelling...

 

Put the cat back on and see if it goes back to how it was?