Unstable / fluctuating rpm during idle

[hotice 0]

Hi all, 

Recently my w204 started having unstable / fluctuating rpm movements (between 800 - 1000rpm), accompanied by a whine each time it fluctuates up. It only happens with the air con turned on, during parking, neutral and drive mode. Brought to a workshop and they said throttle is dirty, recommended a clean up of the throttle body. Another workshop suggested that it could be the air flow sensor / valve. Was wondering if any one experienced the same, and could offer some guidance, please. 

Thanks!