Q: Car is not idling smoothly

asked by on May 13, 2016

My car is not idling smoothly. While idling, it bounces between 700 and 900 RPM. I have replaced the wires, spark plug, and fuel filter. I think I checked the hoses. I also just changed the upper and lower manifold seals. I have noticed that there are small fluctuations when I am driving on the highway while using cruise control and on flat land. I want to solve this myself and not go to a mechanic. Any ideas?

Car idle is rough Inspection $94.99 - $114.99 Get a Quote

Hello. This is typically caused by either a dirty throttle body or a bad throttle position sensor. I typically start by cleaning out the throttle body. That will usually take care of the problem. If it persists, I will use a scan tool to monitor the throttle position sensor signal to see if it is failing. That should be the problem. It can also be the air flow meter, but that is not as common. If you want to have someone take a look at it, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose your idling issue.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing


Experienced Mechanic?

Earn up to $70/hr

What others are asking

Steering wheel locked
It sounds like you may have a problem with your intelligent key and there is a warranty for this item. What happens is the key stop communicating with the car and renders the car useless. There is also some recall...
Car won't stay running
Sounds like you might be having an alternator problem. The vehicle uses the battery to start, once it is running the alternator takes over providing the vehicle with all the electricity it needs. If the alternator fails, the car continues...
Door stuck
Without seeing the nature of the accident damage it will be hard to determine the cause of the door issue. A body panel pushed into the door, like a fender, may be able to be repositioned to restore door operation....
Is it normal for the crankshaft pulley to be stuck if the car is off. The serpentine belt is removed.
The only pulleys you should be able to turn by hand when the serpentine belt is not in place are: the water pump, alternator, and power steering pump pulleys. The air conditioning compressor has a clutch on it that should...
possible misfire or trans/torque converter problem
Try driving the vehicle in regular drive or 3rd gear out of over drive and get to the same vehicle speed and see if the problem is gone. Then try driving to a speed where the engine speed is 1400...
Check engine light flashing at hwy speed
Have a certified technician start off by scanning the system for fault codes. When the check engine light is on (https://www.yourmechanic.com/services/check-engine-light-is-on-inspection) faults will be stored in the system. These faults will give the technician a direction to take do diagnose...
When I have my foot on the gas the truck shakes.
Hi there. Check the air filter and make sure that its not plugged up. A plugged air filter will cause the engine to not breathe correctly and make the engine shake on acceleration. Also check the mass air flow sensor...
Why is 2008 Pontiac grand Prix code reading multiple cylinder misfire
Engine misfires can be caused by many different problems and are generally caused by either a spark or fuel issue or in some cases, a combination of both. Spark related problems generally will result from things like ignition coils, crankshaft...
Slipping
It seems as if the transmission rebuild did not go as planned. I would recommend taking the vehicle to the place that rebuild the transmission initially, and then ask them to see if anything they did may have caused the...

Related articles

2012 Toyota Camry vs. 2012 Chevrolet Malibu: Which One Should I Buy?
Mid-size sedans are the perfect family vehicle; offering just enough space for you and a few kids, but not so much that a small family will feel lost in them. This class of vehicles is slightly larger than a compact...
The Best Used Cars to Buy That Can Be Towed Behind an RV
Summer Summer is a great time for a road trip, but often travelers like bringing all the conveniences of home along, in the form of an RV. Then they tow their car behind it – sometimes this practice is called...
Symptoms of a Bad or Failing Camshaft Position Sensor
Common signs include the Check Engine Light coming on, the vehicle not starting, and an overall reduction in vehicle drive quality.