For the most consistent temperature and the most even cooking, leave the lid of the grill closed as much as possible. That way, the corn will bake as it is grilling and become nice and tender. Only lift the lid every few minutes when it is time to rotate the corn, then close it again immediately. All that being said, if you don’t have a lid on your grill for some reason, you can still grill your street corn successfully. It might take a few more minutes due to heat loss but you will still have delicious charred results in 15-20 minutes. Keep rotating every 3-5 minutes, checking the kernels for tenderness.