It all depends on the engine design, the quality of gas used, etc. Steps 1 and 2 typically do not have to be done more than once every 10,000-15,000 miles, while a quality fuel additive like Step 3 (or part #2616 ) should be run every 3,000-5,000 miles. Your vehicle will often let you know if it’s time. If you have rough idle and hard starting, it might be time for Step 1 again. If you hear knocking/pinging, especially if your vehicle has a high-compression engine that requires an octane value greater than 87, then it’s time for Step 2. If your vehicle is running rough or your mileage is starting to drop even though your driving habits haven’t changed, then it’s time for Step 3.