1991 80 2.0 engine stall with clutch disengaged

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Hi. I'm having problems with my audi 80 , 1991, petrol, 8v . When i declutch and the car is still moving the revs drop below idle and sometimes the engine stalls . I'm also expiriencing some lack of power and a bit higher fuel consumption . I can't seem to find any vacum leaks , I've changed the lambda sensor , spark plugk , leads , distributor cap and rotor , cleaned and recentered the air flow meter ... no change . The only fault code I get is related to the vehicle speed sensor . Running out of ideas ... could it be the Idle air control valve ? Any other suggestions ?

Thank you.