It sounds like you actually didn't fix your root problem. You probably have a slow head gasket coolant leak that's fouling your plugs. You are making it sound like the new fuel injectors helped but they really didn't. You wasted time and money and it still is not repaired.

really..."superimposed EMI".. lol.
There is no "superimposed" anything.
Your problem is either a slow leakage or a blockage in one or both of your VVT solenoids. The blockage prevents proper oil pressure and operation of the VVT on startup. Eventually pressure does build up and the car runs fine ...