S40 2004 Classic 1.6 petrol: fuel gauge issue

[Ashash]

Hi everyone, I hope someone can help me? After switching from a full tank of E5 fuel to E10 from Esso rather than Texaco, my 2004 old shape, s40 Classic started whet I can only describe as ‘pulling’ & a feeling like it may stall when driving. I put in some fuel cleaner and it improved for 1 journey, but returned to the same behaviour v soon after. My fuel gauge then went from half full to empty & gave me a panic! It repeated strange behaviour of misreading fuel levels intermittently, sometimes returning to normal after a few restarts. I have had the fuel tank dropped, the sender unit (pump) replaced, reassembled and checked for leaks. The fuel gauge still behaved oddly. Not long after this a swine tried to steal my catalytic converter, got distributed & left me with a v noisy car & I had to have a new catalytic converter, centre and rear box as a result. My engine light has been on ever since. My fuel gauge doesn’t work at all & is permanently in empty & warning light. The car still does the strange ‘pulling’ & ‘I may stall’ actions, which especially happens when it has a full tank (as before), On the last 4 journeys it hasn’t pulled or stuttered & I’m assuming it’s because the amount of fuel is low (no idea how much fuel I have as I have done 185 miles since filling it up). It does rev slightly when idle, but it’s only done this twice & it wasn’t a major over rev. I have no idea what to ask my local garage to look for! Any help gratefully received!