I have a ford Fusion 2007 SE, and my question is that my car is vibrating heavily now and then(for 1 sec, then stopped for 10~15s then comes back, on repeat) when its on gear( and heater/AC on, sometimes it happens even when its off), I feel the vibrations when stopped, my RPM does go down a little but not so much then goes back after the vibrations. But when my car is on neutral and Park, there is no vibration whatsoever. Do you think that this is a sign of a vacuum leak? or something else?

Need to start with getting codes from the car's computer - then start diagnosis

did check the codes from repair shop just to diagnose it, doesnt really show anything what so ever.