My 2000 Expedition hesitates and stalls most frequently when making a left turn on 2000 Ford Expedition

Mostly in hot humid weather, but can happen at anytime. Ford techs in both Atlanta and Charlotte cannot id problem. No code generated. Best guess resulted in IAC replacement. Did not solve problem. Vehicle has been meticulously maintained. All service performed. 135k mi. One owner. Anybody out there have a better guess?

Asked by for the 2000 Ford Expedition