You don’t indicate the type of transmission that you have, but with a manual the idle RPMs shouldn’t really matter. If it does there’s something goofy in your tune. With an automatic though it makes sense, as you’re increasing the differential between the input and output portions of the torque converter, thereby increasing torque multiplication. The downside to raising the idle speed is increased fuel consumption and in the case of an automatic transmission increased heat load on the engine/transmission when at idle.
A forum community dedicated to Ford Mustang owners and enthusiasts. Come join the discussion about performance, builds, modifications, reviews, engine swaps, classifieds, troubleshooting, maintenance, and more!