Rough idle and miss fire

Having some issues with my brothers passat. Its an AVF engine code. Getting a fault code for a misfire on cylinder 3 and when I check the injection quantities in measuring block 13 cyl 1 and 2 are -3.01 and 3 and 4 are +2.99, torsion value is 0.5

So far I have replaced the injector loom, checked the adjustment of the rockers for the injectors, checked the cam and there is only a small amount of wear on the lobe of cyl 4 exh.

Any suggestions on what to check next

Also it has a fuel heater on top of the filter that uses engine coolant. Are they know to fail and leak water into the filter?