Nissan Sentra 2001 GXE- Engine/car vibrates

[willnissan]

I have a 2001 Sentra GXE (1.8) with 195k miles. I bought it from a relative 2 months ago and i have performed most of the maintenance. Change engine oil, spark plugs, coils, connectors to the coils, cleaned MAF sensor, changed MAF sensor connector, brakes and air filter. Currently, the car does not have any codes when i plug it to the OBD scanner. However, whenever I have the car on Drive with the foot on the break, the car idle stays at 500rpm and the engine vibrates hard. If I turn the AC off, the idle stays at 500rpm and the vibration is reduced by about 70%. Also, if i put the car is in Neutral the car does not vibrate with or without the AC and the idle speed stays at 750rpm. I checked the engine mounts and all of them are fine. I took it to the mechanic and he could find what is wrong with it. Any ideas? Thanks.