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In another thread I mentioned I had this code, but it was more to do with the warranty, which my car escaped, so I thought I'd start a new one. Tonight, while idling at sonic, the car jumped or shook and I quickly turned it off. It started fine and didn't do it again. I read most the threads regarding this code, but I didn't see this symptom. Here is the read:

P0420
Catalyst system below efficiency threshold bank 1
Explanation faulty catalytic converter
Probable cause
1 rich air/fuel ratio
2 air leak near HO2S (heated oxygen sensor)
3 faulty fuel control HO2S (heated oxygen sensor)

Could a bad oxygen sensor cause a spastic idle for a second or two and then even out?

Thanks!
Sandy
 

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Hold on your P0420, this is a real nuisance code.

A bad O2 sensor would not have likely caused your problem, likely you had an engine misfire caused by problem spark plugs, ignition coil or plug wires.

O2 sensors usually do no fail the fix themselves.

In order to really condemn an O2 sensor, it is best to graph them from cold start for the first 4 minutes.

See attached graph where Bank 1, Sensor 1 should look like Bank 1, Sensor 2.

See if you have any misfire codes with Freeze Frame data. Post the Freeze Frame data for review and comment.
 

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Discussion Starter #3
jfoj, I should have stated I had that read at Autozone. I'm an old lady, well a little old, :) that doesn't know much about cars other than what I read about. I used to replace minor things on my 72 Nova, but that was many years ago. So. forgive me, but I have no idea what you just said, but I'm thinking it has to do with reading the codes. But, I do thank you so much. I wish I knew more.
 

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That code usually points to a failed catalytic converter, though it can also be an O2 sensor.

I agree though that I would maybe try to get the car scanned again. It does sound like a misfire that you experienced at idle.
 

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Good stuff

Hold on your P0420, this is a real nuisance code.

A bad O2 sensor would not have likely caused your problem, likely you had an engine misfire caused by problem spark plugs, ignition coil or plug wires.

O2 sensors usually do no fail the fix themselves.

In order to really condemn an O2 sensor, it is best to graph them from cold start for the first 4 minutes.

See attached graph where Bank 1, Sensor 1 should look like Bank 1, Sensor 2.

See if you have any misfire codes with Freeze Frame data. Post the Freeze Frame data for review and comment.
Hey this is good stuff jfoj............If we knew how to read it or figure out what we're looking at..LOL :p I have a vagcom program on my laptop I just don't know how to use it too well. too busy fixing my other cars I don't mess with babyblue too much anymore. besides that pesky code P0420 has not showed it's ugly head lately.........going on two months now.:D


Well to answer sandyl thread I think she just needs to do a tune up, clear the codes and see if it stays gone. she has probably never had her throttle body valved cleaned. I would check all the systems that pertain to emissions.....anyone of those could cause that pesky po420 code. switch to better gas and monitor your engine temperature like jfoj says.
 
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