Light your grill and set to high heat. Oil the grilling grate with sunflower oil.
While grill is heating, make the dressing by combining the mayo, sour cream, cheese, chili, garlic, and cilantro. Set aside.
Place corn over direct heat if using charcoal and high heat if using a gas grill. Rotate occasionally until the corn is cooked and is charred on all sides (this should take about 8 minutes).
Spoon dressing over the corn and evenly coat. Sprinkle with extra cheese, chili powder, and cilantro. Serve each ear with 1-2 lime wedges.