[Capri306]

I'll be the first to say welcome to MW!!!

Okay, with a code 31 it's usually the sensor that needs replacing and nothing else. The original Ford-designed unit has a relatively short service life compared to most any other sensor on the car, as we've found. Wells makes a nice replacement unit, but any reputable brand at most parts stores will work just fine. I remember the code 31 meaning that the EVP (EGR valve position) sensor voltage is below limit, BTW. None of your modifications should cause that code, either.

When you say, "new electronic ignition system," what do you mean by that? Tell us exactly what you replaced.