Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and spread the coals evenly over half of coal grate. Alternatively, set half the burners of a gas grill to high heat. Set cooking grate in place, cover gill and allow to preheat for 5 minutes. Clean and oil the grilling grate.
While coals heat, combine mayonnaise, sour cream, cheese, chili powder, garlic, and cilantro in a large bowl. Stir until homogenous and set aside.
When grill is hot, place corn directly over hot side of grill and cook, rotating occasionally, until cooked through and charred in spots on all sides, about 8 minutes total
Transfer corn to bowl with cheese mixture and use a large spoon to evenly coat corn on all sides with mixture. Sprinkle with extra cheese and chili powder and serve immediately with lime wedges