Once the correct idle mixture has been established, reset the idle speed. In most cases you'll find that balancing the idle mixture will increase the idle speed considerably. Reduce the speed to an rpm range that allows the engine to idle properly. If the Corvette is equipped with an automatic, it should be capable of idling slowly in gear. Keep in mind that "slow" could mean an idle speed of 1,000 rpm if a large duration camshaft with a lot of overlap is used.