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Rough idle

Tiny
NATEGZ
  • MEMBER
  • 2005 FORD MUSTANG
  • 4.0L
  • 6 CYL
  • 2WD
  • MANUAL
  • 170,000 MILES
Rough idle after startup once rpm's drop down. New plugs, wires, coil, fuel pressure regulator, fuel filter.
Do have a code for catalyst bank 2 low efficiency.
Sunday, October 20th, 2019 AT 4:40 PM

12 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Hi,

We need to check for vacuum leaks first. I am not sure the code you have is related but it can be, so can you tell me the actual code? Was is P0420?

Here is a guide that will help with finding a vacuum leak. Let me know what you find and we can go from there. Thanks

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
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Monday, October 21st, 2019 AT 3:50 PM
Tiny
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Okay, actual exact code is po430 for bank 2 below efficiency. And I did just check for vacuum leaks with carburetor cleaner with engine cold and warm with no change in idle while spraying it. I have changed 02 sensors(all4) I just ordered Motorcraft OE plugs to see if that's it, also because I put in NGK plugs that AutoZone sold me and no change with them either.
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Monday, October 21st, 2019 AT 4:37 PM
Tiny
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Also when running live data it seems that my o2 sensor on bank 2 downstream sensor is jumping voltage all over as to bank 1 sensor 2 is stable at.6 volts.
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Monday, October 21st, 2019 AT 4:39 PM
Tiny
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Okay. This code is telling you that the converter is not reducing the harmful emissions like it is supposed to. It can tell this by monitoring the upstream and downstream sensor and it needs to see an increase in oxygen. If it does not then it sets this code. This could be just a faulty sensor but if you replace them then the next most likely cause is the converter itself.
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Tuesday, October 22nd, 2019 AT 5:51 PM
Tiny
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Okay, so would this give me the rough idle and misfire during idle once warm?
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Wednesday, October 23rd, 2019 AT 12:22 AM
Tiny
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It could. It is not common but it could.

Have you check for exhaust leaks also? Normally this code will cause a rough idle when cold so the fact that your vehicle starts that when it is warm points to an o2 sensor issue. Not necessarily the sensor itself but what the sensor is telling the PCM. This could be caused by a faulty sensor giving wrong info or it could be a good sensor just telling it that there is an issue.

The fact that it doesn't start running rough until it is warm means it is going into closed loop which means it is making adjustments based on the o2 sensor data. If there is an exhaust leak then the PCM would start reacting on that data after it is warm.
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Wednesday, October 23rd, 2019 AT 7:29 PM
Tiny
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No leaks in exhaust system checked that also, when watching live data of the o2 sensors bank 2 sensors 1 and 2 mimic each other as where bank 1 sensor 1 is up and down and sensor 2 is.6volts steady. So it is definitely a bad catalytic converter on bank 2. But hopefully that's the cause of bad idle and my AFR is 13.79.1 and not 14.7.1. So there is something throwing it all off.
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Wednesday, October 23rd, 2019 AT 9:14 PM
Tiny
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I think you got it. A catalytic converter issue will effect the air fuel ratio so if that is off then that is the cause of the rough idle. Clearly, let's fix the cat efficiency code and then retest the rough idle. However, I think you will fix both once you fix that code.
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Thursday, October 24th, 2019 AT 3:02 PM
Tiny
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Thank you for your help. I'll keep you posted.
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Thursday, October 24th, 2019 AT 5:53 PM
Tiny
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Sounds great. Thanks
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Thursday, October 24th, 2019 AT 8:12 PM
Tiny
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So just an update: I found the source of the rough idle, it was inside the EGR valve. On the top plastic housing these a little foam filter and it was super dirty. I cleaned it out with soap and water dryer it out and idle is smoother. Still have catalytic converter code as of now.
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Sunday, October 27th, 2019 AT 3:44 PM
Tiny
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Okay. Great. Glad you got it straightened out and it was little to no additional expense. Thanks for the update.
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Sunday, October 27th, 2019 AT 5:19 PM

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