A. Excessive idling quickly adds up to several hidden and not-so hidden costs. In addition to excess fuel waste, idle cars could experience increased maintenance expenses, risk of fines, and even damage to a company’s brand. In terms of maintenance, idling not only produces sulfuric acid, which can eat away at key elements under the hood, but it can also result in: soot buildup, reduced engine efficiency, and contaminated oil. Contaminated oil leads to shorter oil life, and more frequent oil changes.