The injectors themselves have a general lifetime of no more than 100k km. They'll work more than this, but under 100k is when they still operate in factory params. Then again, you cant trust sh*t nowadays cause i installed 4 brand new oem injectors in mine and one failed after a month...
Injectors generally fail by leaking or getting stuck open/closed. They are engineered with very small tolerances so once they get dirty inside, that's the end of them. you also cant really clean petrol injectors because of mechanical wear. To get a matching set of 4 injectors that all spray in the same pattern and the same volume, you need to refurb about 14 injectors at least.
Another thing that fails about them is the filter at the top. It literally disintegrate and get's sucked into the injector. OEM filters last about 60k km or less so most people opt for mesh baskets instead.
Now regarding misfires, it could be caused by many things. My misfires under WOT were caused by a sticking injector while my current misfires at idle are caused by mechanical wear inside the engine. Specifically, my camshafts are rusted and pitted. During idle, cyl 3 misfires 90% of them time.
Other likely causes are spark plugs, ignition coils, valves that arent sealing properly, carbon buildup on the valves and in the intake, faulty pcv system, faulty maf, or a vacuum leak. Plus billion other things...
My advice is, as long as it runs and doesnt have issues during WOT, dont try to fix it lol
