| Cable/throttle assembly seems the likely one, also check the mechanism on the belmouths, see if that is moving freely, there's plenty of adjustment on there, no idea what does what, but check it's all tight, and hasn't worked loose, causing more fuelling etc.
It could be the ECU/Electrical, but I would guess it's more the cable, it hasn't been down the road etc, has it? | 
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