| This happened to me about a year ago. It turned out to be the foam inside Air Filter (aftermartket - without an internal support frame) got sucked in and jammed the butterfly open. It would only happen after a blast with the throttle wide open and would un-stick by blipping the throttle a couple of time's to release. I however found out the hard and expensive way what the problem was - still have the scars ! | 
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