If the misfire is persistent at idle, it's more than likely a bad injector. They just wear out with age and the higher pressures commanded from remaps tends to finish them off. Injector 3 went on mine at ~80K and also just after a remap. I just threw a new set of 4 in. Dealer ones, not ebay or cheapy online suppliers, just to guarantee I wouldn't have to repeat the job after 10,000 miles because it's a right f'cker of a job.
Ideally you do need to see what the fault code is and if it is a bad injector, you want to resolve it sooner rather than later because these engines don't tolerate running lean for long. The top piston ring over heats, closes up and the cracks the ring land, meaning new piston(s) time.