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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: CD player won't accept CDs after I removed the one in it

Hello. If this issue occurred after you removed a CD that was previously stuck, then it is likely that the CD player or drive has failed or jammed. Usually the only way to remedy this issue is to replace...

Q: Brake line leaks

Over time the rubber parts in the braking system will start to leak due to age. If the brake line is leaking then it needs to be replaced. Keep in mind that brake lines should be replaced in pairs. You...

Q: Starts but does not run for very long

I would recommend checking and cleaning your mass air flow sensor as this can cause a lean or rich fuel mixture when not working properly. With this happening, there should be a Check Engine Light on that would have registered...

Related articles

P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.