Diesel Car Idles Rough but Drives Smooth

When your diesel car idles rough but drives smooth, your spark plug might be part of the rough idle causes. It could also be that the water in your gas tank has reached a significant level or it might even be due to a merely clogged air filter.

All these probable causes make your vehicle have a rough idle each time you start the engine, but then runs smoothly when you begin to drive.

Now how do you tell which is actually the cause, Your vehicle idles anytime you turn on the ignition system, and the engine begins to operate. Now that time when you haven’t engaged your gear and your leg off the throttle; this period is known as the idling.

Usually, idling is very smooth, with minimal noise, steady and slow. Continue reading up to find out more on rough idle causes.

Why Does My Diesel Car Idles Rough But Drives Smooth

If your vehicle has a rough idling but still drives smooth, a number of reasons for this include;

  • vacuum leak
  • faulty spark plugs
  • dirty fuel injectors
  • faulty PCV value
  • air filter, EGR valve
  • head gasket leak
  • oxygen sensor
  • bad fuel pump

To get rid of this issue in your vehicle, you need to inspect these parts. Change or maintain them if you can.

Engine parts like your spark plugs can accumulate dirt over a period of time, especially when you have a smoky engine.

However, it is a quite straightforward case as you will be able to easily remove the spark plug. You can either get it cleaned or replaced to get your vehicle functioning as normal.

You need to cultivate the habit of changing your spark plug after every 20,000 miles run; this would avoid issues like rough idling from happening. Another common cause is the fuel injector cleaning additives that you introduced to your gas tank to clean up the carbon build-up in your engine.

A clogged air filter also plays a part in making your vehicle have a rough idle. Like humans, vehicles need to take in air. This air is used for gas combustion in the combustion chamber. For proper combustion to take place, the fuel must be clean and the air-to-fuel mixture ratio must be moderate; otherwise, your carburetor will be gone.

If you have a diesel truck, this also goes for you. The causes of rough idling in a diesel and petrol vehicle are much similar. So yes, if your diesel vehicle idles rough but drives smoothly, the faults can be one of the mentioned causes.

How can I fix a Rough Idle in Your Car?

Rough idling usually happens when you have a cold engine or hasn’t been used for a long time.

Still, it could happen at any time. You need to have the right tools, and experience to diagnose the problem that might be the cause of this issue.

To fix this type of issue. The first thing to do is to ensure that your car’s air filter is neat; if clogged, please replace it immediately. You might also want to scrutinize other places for leaks in your vacuum hoses, diesel or fuel line, or the air intake hose. This can help in determining the real problem that needs to be solved if you don’t have any other engine problems.

If you are not having any success with this process, then you should take your vehicle to a mechanic for a complete vehicle scan and fix. You can also try these steps below before you go to your mechanic.

  • Check if you have anything clogging your engine air intake
  • Ensure that your thermostat is at the right temperature
  • Take out any obstruction or hindrance around the throttle
  • Observe loud sounds

It is annoying to be stuck in traffic, and your vehicle’s engine refuses to start. But this issue is super easy to get rid of, so you don’t need to bother much.

Will a Vacuum Leak Lead to a Rough Idle?

If any of your hoses begin to leak, it will develop a lean gas condition that will cause rough idling due to the occurring engine misfire.

Sometimes, vacuum leaks can also be caused when you have a leaking vacuum supply tank or intake manifold gaskets.

After some years of usage, and exposure to high temperatures, your hoses will most likely develop cracks, and wear down; they might begin to leak depending on the extent of the damage.

When you have too much oxygen disrupting the balance of the air/fuel mixture it can lead to rough idling, high RPMs, and misfiring.

You should have a mechanic examine your hoses for any leakages or cracks after 50,000 miles of the run.

What Can Cause a Car to Shake While Idling?

Once you have a faulty engine seat or mount, you will suffer a major shaking of your vehicle whenever you drive. A bad spark plug loses its ability to give the right amount of sparks.

In this case, the plug cannot ignite your engine. This also goes for loose motor mounts; they can also be responsible for a shaky vehicle.

Your engine mounts are made to secure the engine compartment to the vehicle chassis. You ought to change your plugs or engine mounts immediately if they appear worn-out, in order to avoid shaking your vehicle and any further damage.

Can A Bad Air Filter Cause Rough Idling?

The straightforward answer to this is YES. The function of the air filter is to clean the air that goes into your engine.

As we stated before, the engine needs air too just like humans in order to function effectively.

When you have dirty air flowing into your engine system, it damages and reduces the engine performance and power. So this means that if your air filter is bad, it will have a direct effect on your engine functionality, hence causing rough idling.

Final Thoughts

Rough idling is a vehicle problem that has a lot of probable causes.

Now you can detect a rough idle, and how to handle such situations. Know that a bad spark plug and air filter are one of the most common causes of rough idling in a vehicle.

If you have any concerns on this issue, we will gladly give as much assistance as needed to help you out.