I have a 2002 A6 3.0L CVT. The car was driving perfectly fine. One afternoon, I started the car up with ease, when I reached a stop sign at the bottom of my hill, the car had a rough idle and then died. I started the car up again and again it had a rough idle and then died shortly after. I started it again and backed the car up back into my driveway.

My first thought was a misfire, because of the rough idle. So I checked to see if there were any codes. And sure enough, there was. The four codes were:

P0421 (Warm Up Catalyst Efficiency Below Threshold Bank 1)
P0161 (O2 Heater Circuit Bank 2, Sensor 2)
P0118 (Engine Coolant Temp. Circuit High Input)
P0102 (Mass or Volume Air Flow Circuit Low Input)

So there were no misfires. I looked around forums for a while but couldn't figure out what it could be. I know I need my timing belt service done. And i will probably need new O2 sensors. But I have come across things like vacuum leaks and the worst case scenario...a blown head gasket.

After awhile, I wanted to see if the car continued to have the same symptoms from before, so I started it up and sure enough if was still doing it. The CEL light was on with the same codes and the ESP light was on as well. I also noticed that my coolant level was low and was fine before all this occurred. I didn't drive it long enough to see if it overheated. I refused to take it any where until the problem gets resolved. There were also gas fumes from the exhaust as well as a blueish white smoke.

So I am assuming this is a result of a blown head gasket. If not, can someone correct me and point me in the right direction?

Also, if it is a blown head gasket, how difficult would it be to fix this? I have read that it is a PITA and is best to change head gaskets while doing the TB service.

I haven't done much engine work. I have done simple oil changes, front bumper removal to install new front snub engine mount, and just recently installed all new front upper and lower control arms (8), tie rod ends, and sway bars links. I have also installed new rotors and pads. Would this be enough knowledge to do something like a head gasket replacement. I know I can do the TB service myself.

Money is always my issue and I would rather do the work myself and learn.

Please help me figure this out. I can't keep driving my GF's 02 1.8t Jetta. I neeed my V6.

 

i'd start by checking the oil to see if there is coolant in it.... but it sound like you have one issue possibly causing others...

the coolant temp sensor could cause the 02 issues, which in turn would cause the car to think the maf isn't working or working right....



if i had to change anything listed in the codes it would be the coolant temp sensor

 

It seems like a head gasket let go, but before tearing up things, do a compression test, and if possible a leak down test to make sure. If you are going to fix it yourself, make sure you have a factory repair manual available, or at least subscribe to "Alldata Diy", only $20 for a year, not as good as the FSM, but has all the info needed.

 

If the head gaskets failed suddenly, you'd be the the 1st C5 A6 owner I have heard about having their head gaskets go without a good overheating first.

As mentioned, start with the coolant temp sensor and go from there. Then move onto the air mass meter. If you have a compression tester it's worth a quick test. But I would be surprised if it is the head gaskets.

Did you overheat the engine anytime recently?

 

It hasn't overheated since i purchased it with 70k miles. The only thing is that the temp would sometimes peak past the 190F mark and reach to about 200-210F but then cool back down to 190F. But other than that, no overheating. I bought the coolant temp sensor today as well as a compression test kit. I will be plugging in the new sensor and trying that first. If that doesn't work, i'll try unplugging the MAF sensor to see if the idle gets better. Then if that fails, ill try the compression test. I'll post what happens...

 

Well, I replaced the CTS and the car is still the same, rough idle etc...I unplugged the MAF while the car was on. The car didn't change. So I am assuming it is a faulty MAF? But before I replace this, should the car be warmed up before unplugging the MAF?

 

So with the CTS replaced and cleaned MAF sensor and all codes cleared, the car went straight back to normal. No rough idle, gas fumes, etc. 200 miles have passed with no issues until the check engine lit up. Checked it and its just one code: P0161 (O2 Heater Circuit: Bank 2, Sensor 2)...is this a result of a faulty O2 sensor?