Preheat a grill or grill pan to medium-high heat. Brush the corn lightly with oil.
Grill the corn, turning occasionally, for 10-12 minutes until charred in spots and tender.
While the corn grills, whisk together the mayonnaise and sour cream in a small bowl.
Once the corn is done, brush each ear generously with the mayonnaise-sour cream mixture.
Sprinkle generously with cotija cheese, chili powder, and chopped cilantro, pressing gently so the toppings stick.
Season with a pinch of salt and serve immediately with lime wedges for squeezing over the top.