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Old 06-02-2020, 12:13 PM   #1
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2007 VUE 3.5L
Default Rough Idle, Misfires, Engine Codes P0300 (P0301, P0302, etc.) - SOLVED

Hopefully my troubleshooting experience will be of use to someone else…

Vehicle: 2007 Saturn Vue 3.5L V6 with just over 100,000 miles

Got the MIL or check engine light on the Vue. The only symptom was a rough idle on warmup that had been getting progressively rougher over the last month. It was only rough at idle and for the first five minutes, once warm it idled fine. Even if shut off for several hours it would still idle okay, it was really just the first start of the day with a completely cold engine.

Checking the codes, I had multiple misfires (P0300) and misfires on cylinders 2, 3, 5 (P0302, P0303, P0305). There were some other codes that added to my troubleshooting, but they ended up not being relevant so I’ll leave them out of this write up.

I had already done spark plugs for the 100,000 mile service and I’d also changed one of the oxygen sensors (Bank 1 Sensor 1) in the last year. When I first noticed the rough idle condition, I thought that maybe the other HO2 sensor (Bank 2 Sensor 1) was going bad. I learned that I could pull the emissions fuse to “remove” the HO2 sensors from the system and see how that affected the rough idle condition.

When I pulled the fuse one morning before starting the Vue idled much better. I wasn’t really sure about the quality of the HO2 sensor I had done in the last year (couldn’t remember the brand) and I learned they should probably be done as a pair anyway. Hoping for an easy fix I decided to replace both Bank 1 Sensor 1 (again!) and Bank 2 Sensor 1. Unfortunately, this did not fix the rough idle. So much for my easy fix!

As I continued researching online I came across people with the Honda 3.5L V6 who were having misfires due to tight exhaust valves. Basically, the exhaust valve was staying slightly open (floating) in the compression cycle and unburned fuel was being pushed out the exhaust causing the computer to see a rich condition. The computer would then lean the mixture which would cause a misfire.

Thinking through this scenario I felt it could be applicable to my situation.
  1. Valve inspection and adjustment are due at 100,000 miles.
  2. The rough idle got better once the engine warmed up and I know that sometimes valve issues appear with a cold engine and then clear up once the engine gets warm. This also made me think it probably wasn’t a fuel issue (and maybe should have caused me to doubt my HO2 sensor diagnosis!).
  3. Pulling the emissions fuse clearing the rough idle would make sense because it would cause the computer to maintain a rich condition even if it was seeing unburned fuel being pushed out the exhaust.
  4. I had pulled and cleared the codes several times (as part of troubleshooting the other codes that had appeared initially) and the misfires were always on the same three cylinders. If the exhaust valves were getting tight on those specific cylinders they would always miss during warmup.
At this point I would have loved to go ahead and inspect the valves myself, but I don’t have an appropriate place to do this level of service at my apartment. Instead, I took it to a shop and requested that they inspect and adjust the valves for me. Sure enough they discovered some tight exhaust valves. They also did a diagnosis of the fuel system and recommended a fuel injection service. While I am quite confident that the misfires were due to the valves I figured this couldn’t hurt and probably wasn’t a bad idea anyway considering the age and mileage of the vehicle.

So there’s my story. Not sure that my troubleshooting methods were spot on, but maybe it could help others dealing with misfires. In this case all it really came down to was just getting the recommended maintenance done. Imagine that! Do your maintenance!!
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Old 06-26-2020, 10:09 AM   #2
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2002 VUE 3.0L
2008 SKY Red Line
Default Re: Rough Idle, Misfires, Engine Codes P0300 (P0301, P0302, etc.) - SOLVED

I'm actually going through this on an 02 VUE V6 -- Replaced the Plugs/Coils already and getting ready to replace the Fuel Filter and Clean the Injectors, I bought this used with no idea what level of service has been previously done prior too, It has a 150,000 on it, So I see it as just normal maintenance, Car runs great, Idles pretty good with a slight shimmy, So I guess that's what's throwing my codes.

If that doesn't fix it, I'll look into the O2 sensors next, But I need to brush up on understanding how to read Live Data on the OBD scanner first.
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Old 06-27-2020, 12:00 PM   #3
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Default Re: Rough Idle, Misfires, Engine Codes P0300 (P0301, P0302, etc.) - SOLVED

TJB63, Hopefully you replace the timing belt in that, it was due at 100k.
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Old 07-31-2020, 09:18 AM   #4
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2002 VUE 3.0L
2008 SKY Red Line
Default Re: Rough Idle, Misfires, Engine Codes P0300 (P0301, P0302, etc.) - SOLVED

Hey Blues,

Sorry for the Late reply, Yes, timing Belt and Water Pump replaced. Still getting the Now 'Dreaded' 300-301-303&305 codes, I smoke tested the Vacuum lines, results were no visible leaks, power flushed the fuel rail and injectors, Put a Vacuum gauge on and got a steady at 22, I'm getting ready to do the O2 Sensors next, both Front, I got a feeling the back one will be easier to access by taking off the Plenum, So at that point I think I'll replace the Intake Gaskets.

I'm going to read up on the Valve adjustment issue, Mine is an 02 3,0L as a side note note I bought this back in November 2019 and after a few months I started getting the Misfire codes, It had 149,000 on it when I bought it, So to me the Timing Belt was a priority but since Winter was upon us and I didn't have access to a garage, I had to wait until March to do the belt, I drove it very little until then, and good thing, it was the Original Belt still on there, Interestingly prior to doing the belt, I had a few instances where I'd put it in park and my engine would just start revving into the 5 & 6's, I had read this was related to a switch at the Transmission, Anyhow, part of replacing the Belt I disconnected a few plugs, and of course plugged them back in on reassembly, No idea why, But that issue has completely stopped now.

Hopefully I'll get this Misfire issue fixed, One thing I'm wondering is I used NGK plugs when I did the Coils, I'm considering Re-replacing them with AC Delco's, But i think if they were an issue, My code would be for all Six and not just the same three.

Once I get it figured out, I'll update you, But in the meantime, if anyone has any ideas, I'm all ears.

Oh BTW: my issue has been the opposite of Orins, Runs fine at Start-Up, once it's warmed up, It'll throw the codes at Low Idle either stopping for a Light or sitting Parked with the engine running, and always within 60 miles of resetting the SES Light. Engine RPM is 680 when it fails, that's according to the Live Data I've pulled, My O2 System Bank 1 Sensor 1 gives a jumpy reading, I was getting 0.590 V to 0.055 and all over the place, So I'm hoping that is the problem, Of course I'm not sure what sensor that is, But I assume it's the rear one against the firewall since that is the hardest one to get to.

Wish me Luck. LOL
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