Id look in two areas if you have covered the ignition side of things
1) ECU capacitor causing fueling issues. Carry out a diagnostic check to see if there are any DTC stored. Do you know the history of the ECU? Capacitors replaced before? Worth having ECU cover off to see if there are any capacitors blown and board corroded.
2) Burning / burnt out inlet valve. Carry out a Compression check. Slight leakage on a valve causes a missfire at idle and if the leakage is low will clear as revs rise. If this is the case, dont leave it as damage to the valve and valve seat could turn out expensive e.g. New head
HTH
Steve M
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Its all gone Norfolk!!!
Now in the Lotus position.