Can a Bad Belt Tensioner Cause Rough Idle

Every parts in the engine compartment has important functions they perform. The serpentine belt works perfectly with a tensioner that helps to retain a certain level of tension needed to keep the belt running.

This is to say that without the tensioner, the serpentine belt will lose the tension needed on the serpentine belt. So, what happens when the tensioner goes bad? Can a bad tensioner cause rough idle?

Yes, a bad tensioner can cause rough idle because it will affect the engine timing and cause rough idle. Also, if the tensioner is bad, it will no longer provide the adequate tension needed to the serpentine belt, hence, why the car runs rough on idle and on low speed.

Can a Bad Belt Tensioner Cause Rough Idle?

A bad belt tensioner can cause rough idle if it has gone completely bad. Since the tensioner is responsible for providing the adequate tension needed by the belt to function properly, if the tensioner fails to provide the tension needed, it can cause the car to misfire.

A bad tensioner will not just cause the car to run rough at idle, it will also affect your serpentine belt. As a matter of fact, it can damage your serpentine belt if it’s not noticed and replaced as soon as possible.

Signs of a Bad Belt Tensioner

Here are the signs of a bad belt tensioner:

1. Wear and Tear on your Serpentine Belt

A bad belt tensioner will cause your belt to have uneven wear and tear on it. This is because, the belt has lost its tension hence while it’s getting damaged.

When the tension provided by the tensioner is lower or higher than the minimum, it can cause the belt to wear out faster.

So if you had just replaced your serpentine belt few months ago and it already has some wear and tear in it, I’d suggest you check the tensioner to be sure it has not gone bad especially when the cracks are at the edges of the belt.

2. Whining and Squeaking Noise

Just like a bad serpentine belt, when a belt tensioner goes bad, it can also give a loud squeaking and whining noise. This noise can come in different forms.

For example, the sound may just come on immediately after starting your car for the first time in the day and goes away when the engine warns up. The sound may not come back on again until you start your car the next day.

The sound can as well come on when you turned on your car air conditioner. It may go away after a while or may not. In this case, you should try to check which tensioner is bad.

The sound can also come on immediately you turn your car on and stays on till you off your car. However way it happens, the best thing to do is to check why the sound/noise it’s there and have it fixed.

3. Loose Serpentine Belt

A serpentine belt is designed to hold firmly to its pulleys and rotates evenly. Therefore, when you check the belt and noticed that it’s no longer as firm as it used to be, the tensioner should be investigated.

Driving with a loose belt is not advisable as it can cause your car to lose power. It can also cause other problems to your car hence why you should ensure that whatever has caused the belt to get lose is fixed

4. Old Age

A belt tensioner is designed to last for thousands of miles but not forever. It can get old as a result of old age or maybe because it has been in use for a long time.

When this happens, it will starts to develop cracks and rust around it. So the best solution is to have the tensioner replaced.

5. Engine Overheating

When the belt tensioner goes bad, it can cause the belt to get loose, when this happens, the water pump pulley will not be able to rotate as it should, hence may fail do its job causing your car to overheat.

Overheating is something every car owner should not joke about. It can damage your engine and spoil other things. Therefore, if a bad tensioner is the cause of your overheating problem, it’s wise to have the tensioner replaced as soon as possible before it damages your engine.

6. AC May not Cool Properly

If a bad tensioner causes the belt to get loose, it will no long rotate as it should hence, may prevent the AC from cooling as it used to.

7. Alternator not Charging Battery

The same goes with your alternator. If the serpentine belt is not rotating at its speed because of a loose belt caused by a bad tensioner, it may prevent the alternator from charging the battery properly, hence providing the adequate power needed to run the car. When this happens, your car may start losing its power.

How Much Does It Cost to Replace a Belt Tensioner?

It will cost between $50 to $500 to purchase another belt tensioner depending on your car model and the type of tensioner used. While the replacement cost is $50 to $100.

It is important to use the exact tensioner for your car. Don’t buy one that is not meant for your car.

Can a Bad Tensioner Pulley Cause Rough Start?

Yes a bad tensioner pulley can cause rough start if the tensioner is bad and has caused the belt to get loose. You might find it difficult starting the car and even if it does start, you will experience massive misfire.


Since a belt tensioner is as important as the serpentine belt, it is wise to have it replaced immediately it goes bad to avoid having rough idle at low speed and when you turn on your car.