engine getting better but not quite

[juliet 0]

Well to cut a long story short, as some will have already read on my posts, car has never quite run right, after fitting a new lambda sensor a year ago and so MPG went up to 27 to 30. Then one morning on my way to town the car basically spluttered and died. After disconnecting MAF and doing battery disconnect reset I made it home and have driven around like this for months. But MPG went up to 20 MPG after falling to just 5. also apart from very bad idle or none when you booted it it goes. Today have replaced MAF with working one, new lambda sensor, new plugs new distributor cap and rota arm. Car fired up and admittedly ran a lot smoother than before but still has this under lying problem i.e. ease off throttle and the engine runs on for a couple of seconds, you can feel engine missing when not under load but may be its not missing. Put your foot down and there’s no missing it goes quite well, but and I mean but the MPG has fallen to 8 or 9 MPG. The only other sensors I haven’t changed are Knock sensor, im assuming there’s only 1, sure enough if you disconnect the one i can see the engine dies, other lead next to this appears to go to a crank position sensor, mounted nest to the square oil cooler. I haven’t changed Throttle position sensor could it be this. The only other option is that it does have a uni chip added on next to the existing ECU but i really don’t want to have to go down the option of un wiring this, but could it be a fault with either the uni chip or the existing ECU No point in VAG coming it, this is the earliest of the earliest VR6 cars. Even the wire colours don’t match up in any manual I have. Any help would be most appreciated.

Thanks

Homer