Skip the auto shop - Our mechanics make house calls

Q: Rough/ low idle, smells rich, and has a knocking sound near rear (like exhaust is rattling).

asked by on

Had a local auto store put their computer thing on it. They said the O2 sensor and the knock sensor codes were appearing. Replaced the O2 and spark plugs. Now it has an even worse rough idle and won't keep running or start unless i press the gas pedal.

My car has 200790 miles.
My car has an automatic transmission.

A: Hello. This may be potentially related to t...

Hello. This may be potentially related to the mass air flow sensor or throttle position sensor. Initially, it may have been a faulty O2 sensor, but now since that has been replaced, that part of the system should work correctly.

However, when replacing a part like that, it can cause something else related to the incorrect amount of oxygen being injected into the motor. This is what the mass air flow sensor does. There is also something called an idle air control module that regulates the air flow into the motor at idle. When this is faulty, it can cause the car to also idle roughly. For a more in-depth inspection, I would recommend having an expert from YourMechanic come to your home to diagnose and repair the rough idle.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
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

Get a quote

What others are asking

Q: Passenger's side rear window doesn't work on a 2001 Old Aurora

You hear the noise, that generally means that the motor is still good. So, you probably need a window regulator assembly. Take it apart. I've got a video "how to repair a broken power window" so watch that. They are...

Q: I changed my front mail seal and Harmonic balancer.

The front crank shaft damper is on a key way and it should not matter if the engine moved when loosening or tightening the damper harmonic balancer. The camshaft will move in and out a little bit and this is...

Q: hesitation when accelerating and shaking when in idle

Hey there. A proper diagnosis at a repair shop is the only way to be certain. If the spark plugs have not been changed in 40,000 miles or more, the car would benefit from replacing them. But any number of...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.