Hey Scotty! For the past couple of months my 2012 automatic 3.7L mustang has been trying to die whenever I put it in to park and occasionally when I come to a stop. It only occurs after the car is completely warmed up. The rpms drop below 500 and the whole car shudders then comes back to normal idle. I cleaned the throttle body and the MAF sensor but it only helped for about a week then went right back to it. It has 97,000 miles on it. Please help!
You really need a scan tool to read the codes and data and see whats going on but first... Have your battery and alternator load tested at Autozone and check your spark plugs and Air filter if any of those are bad it can cause that. If check those things and none of that helps you need to take the car to a place that has a high quality scan tool and have them diagnose it for you
Since the problem seems to occur when you stop, it could be a vacuum leak issue. If you have a scan tool, check the fuel trims at idle and then under load. If there is a leak, your STFT will run rich at idle and move back to normal while driving since there will be larger air flow into the engine.
If their are no obvious problems with battery/alternator/plugs/vacuum leaks/air filter/MAF this may be an alternative place to look: Some of the Ford electronic throttle bodies can develop electronics problems with their position sensors and cause the car to surge/stall/die. From what I have read, people will usually start to stall/go into limp mode once it gets bad and the wrench light will flash on the dash. Some people will restart the car and it will be ok (no CEL) for several days/weeks and happen again. I looked on car complaints/various forums and their are several complaints logged:
https://www.carcomplaints.com/Ford/Mustang/2012/engine/engine_shuts_down_while_driving.shtml
Nice video explaining issue: https://www.youtube.com/watch?v=FDpUo3UPmto
Also, you mentioned cleaning the ECB so it may be worth trying an idle relearn:
https://www.youtube.com/watch?v=ZNxXM75zJOw
Good luck
