The MCAS system is different from the autopilot. It is only enabled when the plane is flown manually. There is suppose to be a switch to turn it off altogether. When autopilot is on the MCAS system is off from articles I've read. When the plane is flown manually it has a tendency to lift the nose of the aircraft. The MCAS system forces the nose back down. I am not sure if that is a safety feature or fuel saving feature. I suspect it has more to do with the fuel savings.
The Max has lager engines and are placed forward on the old ones, because to anyone that has flown a 373 the engines are very close to the ground, thus lager engines shorter pylons and set them forward. This makes the wing pitch up due to the normal aeronautical lift but the engines themselves develop lift via thrust. The MCAS detects the Angle of attack indicators on each side of the nose, if these detects the a/c nearing a stall it trims the nose down (only if the flying is done MANUALLY)it also engages brakes or clutches to prevent the pilot from pulling the column back. The Fix is to engage the Auto-Pilot and turn the MCAS OFF (Two switches on the rear of the center console)
I hope this clears up the faulty and erroneous Auto-Pilot issue.
FWIW coming from a former Chief Pilot w/40k Mil and civil hrs