HELP Q7 4.2 FSI Misfires

 
Old 11-03-2014, 04:50 AM
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Default HELP Q7 4.2 FSI Misfires

Hey guys kinda stumped here,

I have a 2008 Audi Q7 4.2 FSI BAR. It has severe misfires at idle and low rpm acceleration.

It is throwing codes for all cylinders randomly. Multiple/random cylinder misfires, never specific to one cylinder or another.

I purchased the car only about a month ago knowing it needed "the O2 sensor replaced" or so said the dealership. The car ran good when I bought it. So, I worked that into the deal and took the car home.

So, when I bought the car, the driver side O2 sensor was throwing codes. Replaced that. Still had another code for passenger side O2 sensor. Went to replace it and found that the wire to the O2 sensor was cut for some reason...so not even hooked into the wiring harness obviously. Replaced that O2 sensor and the misfires got worse.

So, to recap, when car had one bad O2 sensor and one completely disconnected. It ran pretty good.

So, I'm assuming it was in 100% open-loop 100% of the time because of the sensor issues?

Now, it's doing something weird. It will run terrible...misfiring at idle and under acceleration...then the check engine light will begin flashing indicating a new code coming in and it seems it will click over the open-loop again and will run totally smooth for about 25 seconds, then clicks back over and runs bad again.

So far, my thoughts are this:

I pulled a couple spark plugs and checked them and they looked fine. I don't think they are the issue.

I don't think the coil packs are the issue either. Considering the engine has the ABILITY to run perfectly smooth. It just decides to run terrible.

I check for vacuum leaks, there are NONE.

I have read about the carbon buildup problem that occurs in these engines, and, I have not checked, but again, considering the engine CAN run good makes me think that's not the root cause of my issues.

While it was running rough, I unplugged one of the MAF sensors and the idle smoothed out, then agian with the other side. Again, think it's going into open loop.

So, today, I am going to replace both MAF sensors and see if that works...beyond that, I don't know what to do.

Fuel filter?

When it runs good, it runs VERY smooth and strong...

Please if anyone has had any experience with these engines...chime in!
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Old 11-03-2014, 11:06 AM
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Well, I can put this one to bed.

The dealer had the front O2 sensors swapped around...that'll do it!

Last edited by shane0569; 11-03-2014 at 02:15 PM.
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