thanks for your replies
ecu is remapped, fuel pump is quite a new bosche.
no smoke. o2 sensor unplugged doesn't seem to make a diff
afm unplugged - revs at 2k, which is similar to what it was doing the other day reving up to 2k then dropping - so i'm thinking dodgey connection.
opened up the wires that go to plug:
there's an unused bare wire wrapped around 2 AFM wires, and then that's all covered in heat shrink. goes all the way down like that.
connection seems okay though