Posted on 8/28/2026
An engine that idles poorly, hesitates leaving a stop, or suddenly turns on the check engine light can feel like it has a fuel or ignition problem. Sometimes the symptoms even improve once you raise the rpm, which makes the problem harder to pin down from the driver's seat. That pattern is worth paying attention to because air enters the engine where it isn't supposed to change how the engine runs. The leak might come from a cracked hose, intake gasket, PCV connection, brake booster line, or another part of the intake system. A Rough or High Idle Is a Common Clue Vacuum is strongest when the throttle is mostly closed, so leaks tend to have a bigger effect at idle. Extra air slipping into the intake can make the engine idle too fast, surge up and down, or shake as though one or more cylinders are misfiring. You might notice the engine behaves better once you start driving and give it more throttle. At our shop, that difference between idle and higher rpm is ... read more