Ford Focus engine stalls when it's hot outside
I have a 2010 Ford Focus SES with the manual transmission. It has 101k miles on it. The engine stalls after 30 to 60 minutes of driving when it's +85 F outside. It won't start again until the engine has completely cooled off, but will continue to stall so long as the ambient air temperature is elevated. I usually have to wait until the sun goes down before I can limp it home. The coolant temps are normal when this occurs. The engine stalls even under load while driving down the highway.
I can drive this car normally through most of the year, but need to park it during the summer months. I've been dealing with this problem since 2017 and no one I've taken it to (including a Ford dealership) could root cause it. I've replaced spark plugs, air filters, cleaned the throttle body, replaced the purge valve, cleaned the MAF sensor and the problem persists. The car has an aftermarket K&N cold air intake, but is otherwise stock. It came from Denver Colorado and the previous owner supposedly had it tuned, but I don't have any documents to confirm this. I live a lot closer to sea level, so maybe a high-altitude tune is the culprit? I haven't been able to get a scanner on it in the moment and don't know if it's throwing any codes yet.
Any insights are appreciated!