What Causes Idle Shaking After a Car Goes Through Water?
3 Answers
After a car goes through water, engine idle shaking can be caused by a small amount of water entering the high-voltage wires, leading to poor ignition system performance and engine idle shaking, or water entering the exhaust pipe. When a small amount of water enters the high-voltage wires, it can soak the engine's air filter element, increasing intake resistance and allowing water to enter the combustion chamber. This results in poor ignition system performance, and in severe cases, the spark plugs may fail to ignite, causing the engine to idle roughly or even stall. Water entering the exhaust pipe: Open the hood and remove the air filter to check if the filter element is wet, as a wet filter can cause the engine to idle roughly. If the interior is dry, the car can be used safely. If the filter is wet, it should be replaced promptly, and the intake tract should be checked for water droplets or moisture. Precautions for driving through water: When driving through water, shift to 1st or 2nd gear in advance and maintain high throttle to power through. If the water submerges the exhaust pipe, the power will drop significantly. If accelerating doesn't help, maintain high throttle and avoid shifting gears mid-way. After passing through the water, stop the car in neutral, then press the throttle deeply several times to expel water from the exhaust pipe. Before driving again, press the brakes several times to ensure they function properly.
It's really troublesome when the car idles roughly after being submerged in water. I encountered this issue a few days ago when driving into a deep puddle during rain. The next day, the engine shook like it was dancing at idle, making the whole car vibrate. After consulting a mechanic, the problem was traced to the spark plugs—moisture had gotten in, causing unstable ignition. It could also be due to damp ignition coils or high-voltage wires, where moisture disrupts the current flow, leading to shaking. A wet air filter can restrict airflow and affect combustion, while water-damaged computer sensors may send faulty signals, destabilizing idle speed. I recommend going to a repair shop immediately to avoid further rust damage to more parts. Common causes of post-submersion idle shaking include water ingress in the ignition system—timely repairs can save a lot of money, or else the engine might get damaged.
I've encountered many cases of idle shaking after wading through water. Common causes include wet ignition coils leading to weaker sparks, and saturated air filters obstructing airflow and causing uneven combustion. Spark plugs located low are prone to water ingress; when inspecting, first open the hood to check for signs of water accumulation. Short circuits in high-voltage ignition lines can instantly cause shaking—try using a hair dryer to dry the lines. Sensors like the crankshaft position sensor can also send incorrect data to the ECU if wet, and a flooded idle control valve can similarly cause instability. It's best to promptly clear any water accumulation under the chassis to prevent wire oxidation. If shaking occurs initially, avoid revving the engine; instead, drive slowly to a shop for a full scan. For prevention, avoid deep water during rain and regularly check the sealing of spark plugs.
