Doesnt sound right to me, idle air control would give you revving problems, and not always bring on the yellow managment light.
Corsa also have core pack problems.
Is your version the single core pack plugging into all plugs at same time??? if so undo it turn it upside down plug in all 4 spark plugs into the pack , so no plugs in engine . DONT WORRY , get a piece of wire and connect all for plug bodys only togather making good connection and take same wire to anywhere on metal part of engine.
then crank engine and ensure all four plugs spark.
If they are single core pack unplug while engine running each plug one at a time to see which plug doesnt make a difference, thats the dodgy one then
then i would look also at crank shaft sensor or cam sonsor
of course our previous reply could be right , but this test cost no money striaght away.