Fitted a known working S/H DIS pack. The misfire is still there!! Particularly under load (hills or acceleration). Revs fine stationary. I am 99% sure I have put the leads back on in correct order. The old DIS pack looked as new too.
Did the paperclip test and the codes are
21Throttle Position Sensor (TPS) Voltage High
73 Mass Air Flow Sensor Voltage Low and
57Idle Air Control Voltage Low.
Before changing the DIS pack, I tried with the MAF discon to see if it ran better - it didn't. so maybe those codes are a legacy from that as I haven't done 20 or so clean starts.
To date I have had the plugs out, all look the same and were new 4 years ago (say 6000 miles). It had new leads then too and a new DIS pack.
I had a look in the dark and saw a faint amount of blue tracking on plug lead no 5 so I changed that this a.m. for another lead. Still the same.
Is there anything else that could cause a misfire? Poor seals on plenum after cleaning? Stuck lifter? Blocked fuel filter? Partial Vacuum in petrol tank (I'll try the car tomorrow with fuel cap off!)?
I'm really clutching at straws. As ever the car is gutless and runs like a tractor

Any suggestions please?