With over 4-5000 in use the few with any issue are probably less than a fraction of a percent. And most are a vacuum leak or other simple fix. At the most, a tune tweak to adapt for the additional air flow. As with any bolt on, in most cases it is true plug and play needing no tune, but not all cars are equal so the tune tweak needed to optimize is inexpensive and will give you the most out of any mods.
