1996 Ford Falcon Missfire

All stated with flat battery, ECU lost all settings, would not hold revs when gear shift from park to rev found ISC gummed up replaced with new unit also cleaned throttle body all well. NOW when either in drive or park and when engine is up to temp and not before the engine will loss revs the ECU responds by lifting revs up, to about 900 rpm and then resettle to 700 rpm this is repeated in a time cycle if left idling on a 1 min 15 sec or so repetitive cycle ( this is more prevalent in colder months Adelaide SA ) I have replaced the following O2 sensor, plugs, leads, coil pack ( new units). Checked with code checker no codes to report i.E. 111 code ( did this testing during idle stutter ) tested code checker by simulating a fault it was picked up. The engine is not using cooling water, compression test came up OK, have used 91 and 95 octane fuel, sparks plugs all the same colouring, checked tension of intake manifold bolts some where slightly lose. Also disconnected the carbon box electrically to stop the ECU purging the box no change to idle. I also believe the car was using about 13 l per 100 km now using 17 l per 100 km. Things I have checked crank angle sensor, harmonic balancer, timing.