corsa 1.0 misfire at idle

[boddy101]

my corsa just randomly started misfireing at idle the other day. after a short drive, i parked up for about 10mins then went to go out again started it up and it revved like f**k then dropped down to idle then started missing but it revvs up fine and drives good. anyone got anyideas?? the plugs are black but spark and it has good compession and i swapped the maf for a new one but this makes no difference.