Video with multiple angles and before and after shots:

I cleaned this thing using electrical contact cleaner. AFAIK that’s the only thing safe on this sensor. I sprayed that stuff in there really closely on the inside and outside everywhere.

Then I let it dry for 40 minutes before installing, then I probably took a few hours installing it back in and putting the car back together. (I’m slow don’t judge me.)

If you do this, be careful with the valve cover screws. 10 Nm is the torque spec on those.

Also be careful that you fully seat the screw that holds the airbox onto the throttle body. I didn’t torque it enough at first and air was leaking into my throttle from around the airbox. Idk the torque spec, but do just a lil more than hand tight I’d say.

It’s REALLY tight in there. And this is coming from a guy with tiny racoon-like hands. I tried moving the oil dipstick out of the way, but it wouldn’t really budge even after I removed the screw that holds it on the engine. The rest are fuel tubes and injector wiring that I’m not comfortable touching.

My advice is:

  • Do this while the engine is cold.
  • Put a long driver almost reaching the screws.
  • Get your fingers in there and feel the screw.
  • Guide the driver in both from the outside past all the hoses and from the inside. I couldn’t for the love of crap remove those screws any other way. I was at this for like an hour. Total was about 8 hours probably, minus the waiting.
  • Don’t use a wrench. You’ll mess up the screws really fast.
  • Don’t take out the sensor wire out of the sensor. I personally don’t even have a damn clue how to remove it because it wouldn’t budge even while pressing on the tab. You also don’t risk breaking the brittle plastic if you don’t touch it.
  • When you’ve unscrewed the sensor and go to pull it out, it’s kinda hard to take out. Wiggle and pull. I think it’s a bit difficult because of the gasket.
  • Press in the sensor real well when you put it back. It has guides for fitment. Make sure it’s in place before you lose your mind trying to put the screws back in.
  • Don’t touch or brush the inside of the sensor, where the actual sensing tips are. (This is just passthrough.)
  • Spray the cleaner right in there. I don’t think the spray itself can damage anything. Mine isn’t clean fully even after spraying it right in there like 6 times with dry time of a few minutes in between.
  • Don’t let it get this way in the first place. Replace your oil separator every now and then. Idk how often exactly.
  • It’s a PITA to get to it and replace. In hindsight, I’d just replace the sensor.

I will update with whether it fixed the issue or not.

Symptoms were:

  • P0172 (system too rich - latest, seen right before this cleaning)
  • P0170 (generic fuel trim malfunction - cleared at some point and didn’t come back even before this fix)
  • Jerky acceleration especially in lower gears. I could always reproduce it climbing from 1800 to 2200 RPM in 3rd gear with AC off. Also in 1st gear.
  • Hunting at idle (RPM goes slightly up and down by about 50-100 RPM, continuously, in this case)
  • Pretty bad, visible engine vibrations. Much worse than I’ve seen on other 1.4’s online.
  • Sometimes it would even fail to start, but very rarely. Idk if it’s related. I haven’t had this issue in a long while now. Never happened twice in a row.
  • All only happened after a few trips after clearing OBD codes. Right after clearing the codes, the car always felt mint. Hence why I think this sensor was reading bad data and the ECU was adjusting the fuel trims incorrectly.
  • What I would call a pretty high fuel usage for this little twink engine: 5.67l / 100km inter-city (90kmph whenever possible on a long 300km+ trip) and 10l / 100km in the city (not combined). (No AC in both, both during spring or autumn, measured full to full tank when filling at around 10-15 liters probably, that’s how much I usually put in.)

Seen previously:

  • P0401 (EGR circulation insufficient - probably fixed by EGR system cleaning, it’s been like 2 months I think)
  • P0134 (Front lambda sensor no activity - replaced)

Already done, either to fix this or other issues:

  • Replaced the fuel pump
  • EGR system cleaned, EGR replaced and calibrated (I shouldn’t have replaced it I think…a proper cleaning should’ve been enough but whatever…)
  • Replaced spark plugs, cleaned the coils, throttle calibration
  • Replaced oil separator (don’t even try to clean it. It’s a maze inside. You’ll never get all the gunk out, it’s a PITA, and it’s just a cheap piece of plastic anyway.
  • Replaced air filter, replaced damaged airbox parts, properly secure the oil separator -> airbox tube because it was loose
  • Replaced a bunch of engine sensors that were leaking oil according to my mechanic (how the frick does that even happen?)
  • Middle and final exhaust replacement (had mad holes)
  • That’s about it for the stuff relevant to this issue I think, tho I did others too.

Thanks for reading my rant. I found NOBODY online showing or talking about how to clean this specific sensor on this specific engine (AXP engine from VAG). I could find 1.9 TDI’s, 1.6’s, Skoda engines…whatever. But never this specific one. And it seems this one is a fair bit harder to get to because of the location.

I’ll edit the post after a few trips and let you know if I get another check engine light. It will be a few months until then.

  • PriorityMotif@lemmy.worldM
    7·
    5 days ago

    That thing was absolutely filthy, hopefully cleaning it fixed your issues. Thanks for documenting these kinds of issues for others. It’s something I often try to do when I run into an issue which I couldn’t find answers for.

    • 87Six@lemmy.zipOP
      3·
      5 days ago

      My pleasure. I wrote this whole thing only because I couldn’t find this exact situation described anywhere else

  • Onomatopoeia@lemmy.cafeEnglish
    2·
    5 days ago

    Interesting to see a MAP these days. Diesel, I assume?

    As for the leaking sensors - age. Being VW doesn’t help - did the sensors use an actual gasket (like a crush ring). In the Before Times, such things were often pipe thread (a tapered neck and threads) which provided a seal by simply “tightening that thing down”.

    By the 90’s that had pretty much gone away except for some American engines and perhaps VW (maybe on some other European engines). It was an OK approach with a cast iron block and steel bodied sensors, but once we went to aluminum blocks there’s too much expansion for that to remain sealed for the long haul.

    So probably mostly just age.

    Also, good work - cleaning a MAP or MAF is an exercise in patience - they’re both the sort of thing you don’t want to accidentally break while cleaning (it’s an expensive mistake).

    • 87Six@lemmy.zipOP
      1·
      5 days ago

      Not diesel, it’s a petrol engine. No idea why it uses a pressure sensor as opposed to a flow sensor.

      As for the leaking sensors - age.

      Yea a lot on this car is probably caused by that haha

      And thanks! Yea it took a lot of patience all around. I spent a long time trying to take out the dipstick screw and it lead nowhere even after it was out, for instance

      • Onomatopoeia@lemmy.cafeEnglish
        2·
        4 days ago

        MAP systems are technically more accurate, MAF is simpler to design/construct, fewer pieces.

        I think in the Real World there’s not much difference.

        I guessed diesel because MAP is more common on diesel than gas today.

        • 87Six@lemmy.zipOP
          1·
          3 days ago

          Interesting

          I myself haven’t even heard of MAP systems before realizing my car uses one. Took me a while to figure out why the heck I couldn’t see a sensor right past the throttle.