Skip the auto shop - Our mechanics make house calls

Q: Why is my car failing CO levels at idle? It passes everything else with ease.

asked by on

My car's emission report shows that it is far below the maximum allowed gas levels except for at idle, where the CO emissions are twice what they should be. I've replaced the spark plug wires, the plugs themselves, air filter, and I've cleaned all the gunk out of the throttle body and intake. Any ideas as to why it won't pass? I realize its an old engine, but it passes every other part of emissions just fine with no issues. Can you give me some ideas as to what I might replace/ clean or fix to get it to pass?

My car has 200000 miles.
My car has a manual transmission.

A: Hi and thanks for contacting YourMechanic. ...

Hi and thanks for contacting YourMechanic. You may have to replace the distributor cap and rotor for a good, strong spark. Then, get some sea foam and put it in the vacuum system of the engine. This will clean the valves off and help the rings seal better for a cleaner burn.

Change the engine oil and filter for a clean engine. When you take the vehicle to the emissions test, drive the vehicle and get the engine hot like on the freeway, and then keep the engine running until you have to shut it off at the emission station for the test. This will help keep the exhaust hot which will keep the emissions low.

If you need further assistance with your vehicle, then seek out a professional mechanic, such as one from Your Mechanic, to help you make sure your exhaust system is in top condition.

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: The truck is from Georgia which doesn't have smog control. In California it won't pass smog. It has a new motor and transmission.

Hi, the blue-grey smoke you mention is your engine burning oil, probably due to worn piston rings or valve guides and seals. This is expected from an engine with 300K miles on it. Unfortunately for you, California has pretty stringent...

Q: Car starts but dies a few seconds later. If I give it any throttle when it does start it kills the engine.

As a general rule, car engines do not like cold weather and do not do operate as well in cold weather. When you start your car in the morning and turn the key to on, the coolant temperature sensor immediately...

Q: Windows get off track

Hello. For a proper diagnosis, the door panel on the front door will have to be removed. With the door panels removed, the regulator and track will be visible, allowing the mechanic to see what's worn. You may need the...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
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...
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.