FI light coming on ???

Gos, go old school, disconnect the farker and worry about it if the seat of the pants tells you somethings wrong. Warning lights can be more of a pain than help as shit starts getting on
Bit like sore joints as we get older, just ignore it and HTFU

Gos... if you have access to a w'shop manual, there is a test procedure to look at the fault code which is stored in the ECU. Too long to go into here, but I can copy and send. HTH.

The only thing I can think of is maybe it's something to do with the secondary's not being there anymore and the CPU isn't seeing something it's expecting when you're fully on it

aahhhhh yes...secondary's butterfly's....that'd be it.

that makes a bit of sense .....even though the 'spindle' for the secondary 'flies is still in place, and rotating like it should ??

eh..