Why Does a Diesel Engine Shake at Idle?
3 Answers
Here are the reasons why a diesel engine shakes at idle: 1. Stuck fuel injector: A stuck or poorly atomizing injector in one cylinder causes that cylinder to not work or work poorly (blue-white smoke may be emitted from the exhaust). This can be checked using the cylinder cut-off method. 2. Uneven fuel supply from the injection pump: Uneven idle fuel supply from the injection pump leads to inconsistent cylinder operation at idle. 3. Low RPM: Improper idle adjustment (too low RPM) can be resolved by adjusting the idle fuel supply screw. 4. Improper valve clearance: Incorrect valve clearance (due to loose adjustment screws, abnormal wear, or abnormal wear of the valve pushrod) causes the cylinder to not work or work poorly. This can be fixed by adjusting the valve clearance. 5. Poor valve sealing, leading to suboptimal operation. 6. Engine overheating or insufficient oil (causing poor lubrication), making it difficult for engine components to operate smoothly.
I've personally experienced diesel engine idle shaking. That time when I was driving a diesel pickup truck for delivery, the vehicle shook like having malaria at idle, making the steering wheel vibrate. After checking for a long time, I found the most common issues are injector clogging or poor atomization – when the diesel filter is too dirty, it causes poor fuel flow, affecting injection quantity and making the engine unbalanced. It could also be air system failures, like intake pipe leaks or a stuck EGR valve, causing uneven air mixture. Carbon buildup is another culprit; long-term low-speed driving accumulates deposits in the combustion chamber, reducing thermal efficiency and naturally making idle unstable. Worn idle control valves or sensors can also cause trouble – inaccurate feedback signals make the engine "lost." Remember to check if the engine mounts are worn; loose mounts amplify vibrations. For safety, I immediately went to a professional shop for a full vehicle scan, replacing filters and cleaning carbon deposits. Don’t underestimate this small shaking; ignoring it could lead to hidden dangers. Regular maintenance is crucial.
In my opinion, the root cause of diesel engine idle shaking mostly lies in improper fuel system maintenance. Having worked in the workshop, I've encountered many similar cases. When the injection pump has insufficient pressure or leaks, the engine "wheezes" due to inadequate fuel supply. Then there's the diesel filter issue - contaminants blocking fuel lines can obstruct high-pressure fuel pipes. The idle control system is equally crucial; sensors like RPM feedback errors may cause ECU miscommands, or aging/sticking actuators can make idle speed fluctuate. Don't forget that severe engine carbon buildup affects air intake and combustion uniformity. Worn engine mounts can amplify minor vibrations into "massage chair" levels. Whenever this happens, I advise car owners to first try replacing the diesel filter - it often alleviates the problem. Persistent shaking requires electrical system checks and fault code scanning. Unstable idle isn't trivial - sudden stalling at highway speeds is dangerous, so don't skimp on repair costs.
