80 diesel vac pump lower front of engine, left side, petrol only vac from inlet manifold, diesel have a resovoir on inner left wing.
Diesels without a butterfly in the manifold the vacuum is insufficient, plus it would be pressurised from the turbo.
Thinking about it, I have never tried removing the filter cover with the engine running, but the turbo is spinning at idle so definitely a negative signal, of course then to positive post turbo.
Mine is in bits at the moment so cannot check but, a blocked air filter would increase the difficulty in removing the lid.
Regards
Dave