My friend had a Pug 406 with the 2.1 engine, it too had the same same engine and same problem. I know my reply will be vague but maybe some one can expand on it for you....
When this problem happend it was due to a weak spring in the fueling somwhere, what he did was to initially stretch the spring and he replaced it this solved the problem,. sorry i cannot be of anymore assistance.
Phantom Revving
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