Rough Idle - Idle voltage Variation
01-07-2019, 10:31 PM
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2009 C63 AMG, 1998 Nissan Frontier
Rough Idle - Idle voltage Variation
For about 8 months I have had a mild rough idle. Nothing too crazy and no Cel, but every few seconds I feel a shimmy. I have replaced injectors, spark plugs, intake manifold gaskets, cleaned throttles, installed an oil catch can, cleaned O2 sensors, cleaned purge valve, and installed a new interstate battery. The car runs excellent otherwise. There are not any codes stored in the background. While idling I can here a small misfire when the car shakes, sounds like a little pop out the exhaust. I decided to check the voltage on the battery while the car was idling and discovered that the voltage is jumping around some. Even more interesting is that the pops from the exhaust correlate to the dips in voltage. Is this variation while idling normal? Could someone whose not idling rough perform the same test and see if your voltage is stable in comparison to mine? Over a period of 1 minute and 15 seconds the max = 14.26v and the min=13.78v. Thanks in advance.
Last edited by Dtorre1240; 01-10-2019 at 10:05 AM.
01-09-2019, 11:33 AM
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2009 C63 AMG, 1998 Nissan Frontier
No codes. About a week ago the car would not start randomly. There was a very strong smell of gas. I let the car sit 15 minutes and turned the key with the gas depressed and it started. I scanned right after this and there was a p0600 serial communication Link. I cleared that code and it hasn't returned. I do not have Xentry.
01-09-2019, 12:51 PM
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2009 C63 AMG, 1998 Nissan Frontier
What is the purpose of seeing these fuel codes? I wouldn't have a misfire and a voltage dip if the problem was strictly related to fuel. I'm suspecting that the ignition system is suffering due to the unstable voltage.
01-09-2019, 03:17 PM
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You wouldn't have a voltage dip and a misfire without having a code.
The problem must be somewhere where your scanner cannot pick up the code.
Once you see the code, this becomes factual, vs opinion of what this might or might not be.
But this is just what I would do, good luck with troubleshooting this.
The problem must be somewhere where your scanner cannot pick up the code.
Once you see the code, this becomes factual, vs opinion of what this might or might not be.
But this is just what I would do, good luck with troubleshooting this.
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01-09-2019, 03:45 PM
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Good point. From my understanding codes are set when limits are reached. So its very possible the issue is borderline a limit and no codes are set. I had the car multiple times at a dealer for other issues and never did they mention issues that could pertain to this. So either they were aware of it and ignored it or Xentry is not showing anything out of the ordinary.
01-09-2019, 09:04 PM
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Can you post the video? Was the idle RPM changing during the voltage fluctuations? The static pics don't actually help at all.
If there were fuel codes, that could dictate idle RPM changes, that could account for the voltage fluctuations.
If there were fuel codes, that could dictate idle RPM changes, that could account for the voltage fluctuations.
03-12-2019, 08:23 AM
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Well my issue has been resolved. I had a deep cycle boat battery in the car from the original owner which was causing my issue. Swapped to an OEM battery and the misfires and fluctuations have disappeared.
03-12-2019, 01:42 PM
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2012 C63;1971 280SE 3.5(Sold);2023 EQS 450 SUV 4 Matic (Wife's)
Interesting, how did you diagnose the issue with the deep cycle battery type or did you just get fed up and replace the battery. I have read of unusual operating symptoms of deep cycle batteries but never used one myself. I sailed for years and the battery always seemed to be a common point of failure, deep cycle or not. They always sit too long and never get run long enough when under power. They never get a maintenance charge until they are dead and by then they generally have discharged enough that they never fully recover with a dead cell or irregular operating symptoms such as voltage fluctuations. If your car sits for long periods and/or only gets used for short drives it may be wise to get a maintenance charger and use it regularly to keep the battery fully charged and in top condition. This will generally increase the life of your battery and ensure uninterrupted performance.
