A hiss under the hood at idle
An engine that idles rough, hunts up and down at a stop, or stumbles just off idle, and then smooths out once you are moving, often has a leak on the intake side. Air is getting into the engine through a path the engine computer cannot measure.
The engine works out how much fuel to add from the air it expects to receive. A cracked hose, a split intake boot or a failed gasket lets extra air in past that measurement. At idle, when the engine takes in very little air, the extra is a large share of the total and the mixture runs lean. At higher speeds the leak is a small share and the engine copes.
That is why the symptom is so specific to idle. It often comes with:
- A hiss or whistle from the engine bay with the engine running.
- An idle that is higher or lower than it used to be.
- A warning light, often with a lean-running code.
- A rough idle that is worse with the A/C or headlights on.
What helps the diagnosis
Listen with the hood up and the engine idling, from a safe position away from the fan and belts. A hiss you can point toward is useful, and so is noticing whether the symptom is worse when cold or once warm, since rubber parts shrink and crack open more in some conditions than others.
Intake leaks are usually inexpensive parts in awkward places. Finding them is the work, and a good description shortens it.
What this store covers
Diagnosis and repair from one address with nineteen services, so a fault that turns out to involve the cooling system or overdue scheduled maintenance stays in the same building. Confirm the vehicle type when you book. The national engine repair page covers what a warning light does and does not report.
Other stores nearby
Joplin and Osage Beach also offer engine repair.
About this store
The Springfield store is managed by Steve Richardson.
See the national engine repair page for all 33 locations.