This is our favorite dip served at El Toro Loco along with salsa and tortilla chips, and we brought some home so we could attempt to replicate it. The sauce separated after being left out overnight, so there was definitely sour cream in there.
Use a dash of the juice from a jar of jalapeno peppers. You can also optionally add chopped jalapenos, depending on your heat preferences. Mix together all ingredients. The sauce should be lightly sweet and tangy, and have a consistency slightly thinner than ranch dressing. Add a few dashes of sugar to sweeten if necessary, and whole milk or heavy cream to thin it out if necessary. Refrigerate for at least 24 hours. This will meld the flavors and reduce the heavy mayonaise flavor. Serve with warm tortilla chips and salsa.