If you have TBI, then you don't have a carb at all. You have a fuel injection throttle body.
What it sounds like you might have a bad fuel pressure regulator. If the diaphram gets a whole in it, the vacuum will draw fuel through the diaphram into the intake and the vacuum is the strongest at idle. The way you would have to test for that is using an accurate fuel pressure gauge and look for any loss of rest pressure.