I paid $30 to have the fast idle enabled, but feel it was worth the money. We use the fast idle, rather than letting it idle, when stopping after towing the fiver in order for the turbo to cool down. The manual recommends up to five minutes idling to allow the turbo to cool in order to protect the seals. The EGT probe (Edge insight) is installed in the exhaust manifold and we wait for the temps to drop below 400 degrees before shutting her down. When towing the EGT is usually between 11-1200 degrees and when climbing steep hills it can reach 1375, and I have seen it above 1500 for short periods of time when coming out of regen.