Bad O2 Sensor? VAG-COM and APR K04 Question...

[timneedscoffee10]

So I've been having a strange fluctuation at idle at cold-start, and have been suspicious of my O2 sensors or MAF. If I cold start on a warm day, the engine will rev to about 1100 for maybe 15 seconds (per normal), then drop to about 850 and "pulse" between 850 and 1000 rpms until the engine is warm.

This morning I hooked up my VAG-COM and the MAF seems okay (reading 4gps at warm idle), but my O2 sensors concern me. In Block 30, Bank 1 Sensor 1 reads 00111 and Bank 1 Sensor 2 reads 0000.

I assume that sensor 2 is 0000 because APR disables the post-cat o2 sensor to avoid the CEL. However, I expect to see sensor 1 fluctuating between "111" and "011" pretty quickly.

Am I interpreting this correctly - that my pre-cat bad and my post-cat disabled, or are they both bad?

 

[timneedscoffee10]

Just confirmed with APR that they don't shut off the post-cat sensor, so their file wouldn't cause the 0000 fixed reading.

So my question devolves into - am I interpreting this right that I have two bad O2 sensors?

 

[Bronson@APR]

You spoke to me this morning.

Just so you have the information to reference somewhere, we do not completely code out the rear O2. We disable the fault code P0420. This allows functionality in all other instances except for when the rear O2 is trying to measure catalyst efficiency.

I would check for air leaks in the intake tract, I would also check the functionality of the MAF sensor further. Try to run the car without the MAF sensor, see if the issues go away. This will help rule out a metered air issue. I would then try to log the car for a 3rd/4th gear pull with decent resolution and check out instantaneous lambda correction. This will be in block 001, reference this against injection time and load.

Let me know how it goes! :thumbsup:

 

[timneedscoffee10]

You spoke to me this morning.

Just so you have the information to reference somewhere, we do not completely code out the rear O2. We disable the fault code P0420. This allows functionality in all other instances except for when the rear O2 is trying to measure catalyst efficiency.

I would check for air leaks in the intake tract, I would also check the functionality of the MAF sensor further. Try to run the car without the MAF sensor, see if the issues go away. This will help rule out a metered air issue. I would then try to log the car for a 3rd/4th gear pull with decent resolution and check out instantaneous lambda correction. This will be in block 001, reference this against injection time and load.

Let me know how it goes! :thumbsup:

Hey Bronson - thanks for following up! I'll definitely do some more diagnostics on the intake side... But seeing the sensors pegged in their states still seems to indicate bad o2 sensors, doesn't it?

 

[timneedscoffee10]

Tested my pre-cat O2 sensor directly with a voltmeter and it was definitely shot - so I swapped them out this morning. Car is doing much better! Pics of the sensors in my build thread... they looked pretty fouled to me - caked with a layer of carbon, and completely plugged up.

Still, though, the car did the pulsing idle on the first start with the new sensors, but not since then... I went over all the intake and IC piping again and didn't find any leaks. Double checked all the clamps just in case too. Will run with the MAF disconnected to see how that goes, this started within a week or so of the last time I cleaned/oiled my intake filter, so I may have over done it with the oil.

 

[FLtrooper]

I am also suffering front the pulsing idle issue at cold start.. What's odd is my friend with a k04 mk6 recently switched from APR to another big name tuner and said while on APR he had the same issues and instantly after the switch it went away..

I have no CEL or codes via Vag-com and only have 13k miles on the car.

HELP!!

 

[timneedscoffee10]

I am also suffering front the pulsing idle issue at cold start.. What's odd is my friend with a k04 mk6 recently switched from GIAC to APR and said while on APR he had the same issues and instantly after the switch it went away..

I have no CEL or codes via Vag-com and only have 13k miles on the car.

HELP!!

Mine started only a couple weeks ago... Had several thousand on the k04 before it started, so I'm not convinced it's directly related. No CEL or codes here either. I probably won't get to do any data logging this week - cops everywhere for the holiday, and no roads with speed limits past 55. But next week I'll do some logging for the info Bronson requested, and am also going to clean the MAF.

 

[FLtrooper]

I can recall it happening a couple times when first flashed but now its everytime.. Seems to be a common issue with out file after doing a little more research.

 

[timneedscoffee10]

I can recall it happening a couple times when first flashed but now its everytime.. Seems to be a common issue with out file after doing a little more research.

Maybe I'll roll around in stock mode through this week just to see.

 

[Gunkata]

I've had a few rough startups lately, but not sure if there is any pulsing or rev holds.

 

[timneedscoffee10]

So I finally picked up a can of CRC MAF Sensor Cleaner and cleaned the MAF. Didn't realize the MAF itself is held into the housing with two T20 Security Torx bits, but I was able to grab on to the heads with a small pair of vice grips and loosen them with no trouble. Followed the instructions on the can (10-15 sprays with the cleaner, on all sides, and air-dry thoroughly) then went for a test drive.

The "pulsing idle" had been manifesting while cruising, too, over the past several days - I could feel an intermittent kick in the throttle. That appears to have subsided. Too soon to tell if the pulsing idle is gone, as the engine hasn't gotten cold since I cleaned it - but I can definitely feel a difference after cleaning it - which is a positive sign.

 

[timneedscoffee10]

Quick update - the pulsing idle appears to be completely gone!

 

[DarienMidnight]

I got a CeL today ..performance dealer said I had a bad o2 sensor ...but this just started happening after I went stage 2 . Have to check code again if it's P0420. What steps should I take next ?

 

[brobst]

I got a CeL today ..performance dealer said I had a bad o2 sensor ...but this just started happening after I went stage 2 . Have to check code again if it's P0420. What steps should I take next ?

That is the code for when the o2 sensor detects higher flow from an aftermarket downpipe. When you go stg2, it should be coded off. Unless you have some tune for passing emissions. In that case, you need an o2 sensor spacer to try and defeat the cel

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[GroceryGTIer]

That is the code for when the o2 sensor detects higher flow from an aftermarket downpipe. When you go stg2, it should be coded off. Unless you have some tune for passing emissions. In that case, you need an o2 sensor spacer to try and defeat the cel

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For the front o2 ? Or front and rear?