Finally got quite a few of the common faults sorted (mine seems to have landed itself with all of them

Next on my to do list is the flat spot at 1500-2000rpm, i keep hearing its the injector wiring, iv bought a repair kit but only 1. im also hearing its the 3rd injector thats most common but im guessing theres no real way of knowing il just have to do the 3rd one first and see what happens

Mt question is in what way does the wiring/injector plug make me get a flat spot at exactly the same rpm, surley if the wiring was faulty id get a sign that it was knackered at anytime why at these rev, basically can someone explain in a bit more detail whats goin on with this