O2 sensor problems 97 Jetta -- Need quick reply!

Greetings all, my son has a recently purchased Trek edition Jetta that has been running excellent. Now it's crap. He's in the North Bend area of Washington with a cell phone but no internet access, I'm in Alaska with internet. He went to some shop and got an $80 diagnostic with a PO 172 code on it, along with some illegible writing.

Short version, the place wasn't too helpful and he didn't want to spend any more $$ there. A German auto shop has confirmed it "sounds" like a O2 sensor, but they and the dealer say he only has one, he thinks he sees two of them on the pipe, before and after the cat converter. They said the 98's have 2 but his is definitely a 97. He can't afford to troubleshoot by replacing parts until fixed either.

car has 83000 miles, with 2.0 liter motor

Questions are:
Is anybody familiar enough with this model to know what the deal is, was there a model change somewhere in there that would account for that?

If there are indeed 2 sensors, do they need to be changed together or is there a way to know which one is bad, and just do the one.

Is there a reset procedure for the ECU or other controller and is that something one can do theirself? He got an instock NAPA price of $100 for one of the sensors everybody agrees he does have. Does that sound right?

He's currently semi-stuck in this situation, car is running terrible, hence the need for a quick reply. He's pretty capable if it's not too involved a job. he has very limited tools and place to work, and needs to get back on the road ASAP.

My expertise is Toyota PU/4runners and I'm clueless here. The last VW's I had were a herd of old hippie busses and bugs back in the 70's... Thanks in advance!

nobody can afford to put parts into there car that wont fix a problem but they can afford mc donalds and ice cream when they want it.

The split from 1 to 2 o2 sensors is in the 1995 obd1 year. 1996+ cars are obd2 and have 2 o2 sensors. Front o2 sensors are a common failure on older cars with more mileage on them. p0172 is a system too rich condition. It can be caused by a bad front o2 sensor, leaky injectors, bad mass air flow sensor, carboned and oiled up intake and throttle body, and clogged air filter. I reccomend him to manually take off the intake pipe off the throttle body (the pipe that goes from the air box to the engine) and clean off the throttle body and the inside of the pipe with some throttle body cleaner you can find at any car parts store. Just spray all that black oily stuff off the throttle body and open it up and spray inside there some. ALso clean off inside the mass air flow sensor with that cleaner stuff. Put everything back together and start the car with the foot to the floor. It will run rough for a little and smoke some but thats just the engine burning off all that gunk. ALso it helps if the car is warmed up fullu before doing that.

Update: he replaced the front O2 sensor, reset the ECU and car immediately ran much better for a day. He put 80 hiway miles on it right away with no problems except a slight hesitation on acceleration. Today it began to run badly again, missing and sputtering. He has access to a scanner now also and getting the PO 172 code again after clearing it. I'll have him check the vacumn lines and try the cleaner thing. Thanks.

Another mechanic is suggesting the MAF sensor. Is there a specific code for that or is it also covered under the PO172 code?

Try cleaning the maf sensor first, sometimes due to the large amount of oil in the intake it covers the maf sensor causing it to read incorrectly.

Ok, so far so good, the crankcase ventilation valve on top of the cam cover was toast, so a new valve and related tubes later, all's mostly well, except for a nagging slight hesitation on acceleration. MAf was cruddy but cleaned up OK. No new codes. So consider it fixed. Thanks.

One thing tho, I didn't think ANYBODY had more expensive parts than Toyota...!!

yea ... try BMW... or Bring My Wallet

Inside the air box, below the air filter, is a small wire mesh air screen on one of the intakes which can get clogged with dirt over time. The air screen prevents mice, etc, from making a nest out of your air box. Since it's easy to remove (two screws hold it in place), I'd dust it off and see if your pickup comes back. After about 75k, mine was more than half clogged with junk.