Cause: Incorrect engine timing can cause the engine to run roughly and produce a rocking motion. This can occur when the timing belt or chain is stretched or has skipped a tooth.
Symptoms: In addition to idling roughly and rocking, the engine may also stall, backfire, or exhibit reduced performance.
2. Incorrect Idle Air Control (IAC) Settings
Cause: The IAC controls the amount of air that enters the engine at idle. If the IAC settings are incorrect, the engine may run too lean or too rich, causing it to idle roughly and rock.
Symptoms: In addition to idling roughly and rocking, the engine may also stall, surge, or hesitate when accelerating.
3. Vacuum Leak
Cause: A vacuum leak allows air to enter the engine unmetered, which can cause the engine to run lean and idle roughly. This can be caused by a cracked or loose vacuum hose, or a faulty gasket.
Symptoms: In addition to idling roughly and rocking, the engine may also stall, have reduced performance, or exhibit a higher-than-normal idle speed.
4. Dirty or Faulty Fuel Injector
Cause: A dirty or faulty fuel injector can cause the engine to run rich or lean, causing it to idle roughly and rock. This can occur when the fuel injector is clogged, damaged, or the injector's electrical connection is loose or corroded.
Symptoms: In addition to idling roughly and rocking, the engine may also stall, surge, or hesitate when accelerating.
5. Damaged Engine Mount
Cause: Engine mounts are designed to dampen engine vibrations and keep the engine securely in place. If an engine mount is damaged or broken, it can cause the engine to rock excessively when idling.
Symptoms: In addition to idling roughly and rocking, the engine may also produce a knocking or clunking noise.
6. Worn Spark Plugs or Ignition Components
Cause: Worn spark plugs or ignition components can cause the engine to misfire, which can lead to rough idling and rocking. This can occur when the spark plugs are worn out, the spark plug wires are loose or damaged, or the ignition coil is faulty.
Symptoms: In addition to idling roughly and rocking, the engine may also stall, have reduced performance, or exhibit a higher-than-normal idle speed.
7. Low Engine Oil
Cause: Low engine oil can cause the engine's bearings and components to overheat and wear prematurely, which can lead to rough idling and rocking.
Symptoms: In addition to idling roughly and rocking, the engine may also produce knocking or grinding noises, or the oil pressure warning light may illuminate.
8. Incorrect Fuel Pressure
Cause: The engine requires a specific fuel pressure to run properly. If the fuel pressure is too low or too high, the engine can run roughly and rock. This can be caused by a faulty fuel pump, a clogged fuel filter, or a malfunctioning fuel pressure regulator.
Symptoms: In addition to idling roughly and rocking, the engine may also stall, surge, or hesitate when accelerating.
