Ford ka , running, but really juddering, engine light on, on the dash

just changed the plugs, whilst at it compression tested

1. 11.6 bar
2. 11.5 bar
3. 10.1 bar
4. 12.2 bar

iscv reading 9.6 ohms

lamba sensor 4 wires

between 2 white wires 7.8 ohms, no reading ground

grey and black wire give no reading between each other, white wires or ground.

help please