I’ve recently bought a 1985 Mk2 and I’m having some troubles. The car from the factory came with the 8v engine however it has since had the 16v engine dropped in, its also got KJet injection. The problem is that when I’m driving and I go near 4500-5500 rpm or above, the car will stutter and cut out. (The engine will still run but a drone sound comes from the engine when the accelerator is pressed) It doesn’t happen all the time and it’s not always at the same rpm but around that area. The cars had a new alternator and battery and it has made it a little better but the problem persists. A local garage thinks it could be due to me having 3 standard plug leads and 1 BMW performance lead (came with the car when purchased). When the engine jerks and cuts out near the rpm range I can hear a relay (or a number of relays) clicking underneath the dashboard. When the engine jerks, it’s possible to slow the engine down, shift down a gear and the car will make it past without jerking all the way to red line. It’s hard to explain what’s happening but basically when the revs get near 4/5k the car will suddenly start to jolt instead of accelerating. The car won’t stall out but I have to let off the accelerator for it to stop. This will happen either at WOT or just gradually building up speed. What could be causing my problem? Any help is greatly appreciated.