I have had my 2014mkz for only 5 years. For the last year it’s been stalling on a warm start when pulling out of parking lots (going very slow) or if I am idling in a drive thru too long. I have had fuel sensors, air sensors, filters etc. replaced. The car still does this. My mechanic said(I have no car knowledge) they noticed build up on my engine where gas is not being burned off which may be the problem. They told me to use more expensive gas bc it’s cleaner but honestly I cannot afford that at this time. Has anyone else heard that they have more build up on their engine than they should? My mechanic thinks it’s weird bc they don’t see this level of build up on cars under 100kmiles. Mine is at 50k/60k. The only solution is to take to a specialist who has the tools to clean the tiny area deep in the engine to get the build up off, but they have to be super careful to not get the gunk into the engine or it will seize it? I don’t know. It sounds ridiculous.