MAF spec range for 1.8t

[mosnet99]

I'm getting intermittent idle issues and very rarely when it was cold on start up it would stumble right after turning over. My B1S2 O2 is operating in the 1.5V range, I believe that's why my Readiness on Vag was failing. Any way, my MAF is operating between 2g and 17g. Does anyone know if this is the normal range?

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[texasboy21]

Idle should be between 2-4g/s. Peak airflow for a chipped car is 150-170g/s. Stock tune should be in the 130ish g/s range.

[old guy]

Your B1S2 is the rear O2 sensor. Some good information in this thread about how it all works: Clicky click®

[mosnet99]

Idle should be between 2-4g/s. Peak airflow for a chipped car is 150-170g/s. Stock tune should be in the 130ish g/s range.

I noticed my mom's 2.0T idles close to 4g. But I watched mine for a while today after the engine was warm and it was hovering a hair above 2g actually hitting 1.98g once. At idle it doesn't even come close to 2.5g. I'm thinking I need to clean it or get another one.

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[mosnet99]

Your B1S2 is the rear O2 sensor. Some good information in this thread about how it all works: Clicky click®

The switching rate makes sense why a CEL is not thrown now. I didn't think O2 sensor operate around 1.5V that's what alarmed me not to mention groups 34, 37 & 43 will not pass in Basic Settings. Is the B1S2 hard to R&R ?

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[Manutdfan1]

Really though IT depends on How long its rough for, you cant depend in an O2 for anything unting IT has time to warm. If the engine is warming up you need to focus more on the ETC. This has priority until he O2 is heated up. Just my thought but what do I know lol...


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[Manutdfan1]

Wow you would think English is my second language, had other language selected, sorry about the spelling !!!


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[Manutdfan1]

And the b1s2 is just a monitor O2, it shouldn't toggle. Should be around 1.5 steady. That sensor is watching the converter to see its working. If it was replicating the pattern of the front O2 you would have a cat convert issue.


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[old guy]

And the b1s2 is just a monitor O2, it shouldn't toggle. Should be around 1.5 steady. That sensor is watching the converter to see its working. If it was replicating the pattern of the front O2 you would have a cat convert issue.

You are correct in that a rear O2 sensor that switches excessively indicates a bad cat. However, the 1.8T has a B1S1 wideband sensor so you really can't compare the voltage of the wideband with the B1S2 rear O2 sensor. And the rear O2 voltage shouldn't be anywhere near 1.5V. Typically it should be closer to and slightly above .47V.

[old guy]

To Mosnet99: I assume you are getting a DTC for the rear O2 sensor. What exactly is the DTC?

In your first post you mentioned that your MAF sensor had a range of 2 g/s to 17 g/s. Please explain the conditions of that range. Is that for a cold start when your idle is high and then drops?

If you are getting 2 g/s and lower at idle you may want to first clean the MAF sensor before going any further. Another possibility for a low g/s accompanied with a rough idle could be a result of a very small vacuum leak. Check your STFT and LTFT. A high adjustment in the STFT at idle would indicate the the ECM is adding fuel to adjust for the false air condition where some of the air is entering the intake after the MAF sensor.

[mosnet99]

To Mosnet99: I assume you are getting a DTC for the rear O2 sensor. What exactly is the DTC?

In your first post you mentioned that your MAF sensor had a range of 2 g/s to 17 g/s. Please explain the conditions of that range. Is that for a cold start when your idle is high and then drops?

If you are getting 2 g/s and lower at idle you may want to first clean the MAF sensor before going any further. Another possibility for a low g/s accompanied with a rough idle could be a result of a very small vacuum leak. Check your STFT and LTFT. A high adjustment in the STFT at idle would indicate the the ECM is adding fuel to adjust for the false air condition where some of the air is entering the intake after the MAF sensor.

I'm actually not getting a DTC on the rear sensor, I'm thinking because its still switching even though its out of the voltage range. The conditions in which I got the MAF readings were the engine was well beyond being warmed up (after 20 min trip) and throttle was idle to around 4K rpm. I'm going to check my STFT and LTFT today.

[mosnet99]

To Mosnet99: I assume you are getting a DTC for the rear O2 sensor. What exactly is the DTC?

In your first post you mentioned that your MAF sensor had a range of 2 g/s to 17 g/s. Please explain the conditions of that range. Is that for a cold start when your idle is high and then drops?

If you are getting 2 g/s and lower at idle you may want to first clean the MAF sensor before going any further. Another possibility for a low g/s accompanied with a rough idle could be a result of a very small vacuum leak. Check your STFT and LTFT. A high adjustment in the STFT at idle would indicate the the ECM is adding fuel to adjust for the false air condition where some of the air is entering the intake after the MAF sensor.

https://drive.google.com/open?id=0B7...mcteWdGTW9aTm8

This is at highway speed and part throttle

[old guy]

Block 32 is your LTFT. Block 33 is the STFT. This will help explain the LTFT and STFT.

[mosnet99]

Block 32 is your LTFT. Block 33 is the STFT. This will help explain the LTFT and STFT.

Okay so The LTFT under load when I started was 6.2 (a bit high) but the idle LTFT was on spec at .8. So I cleared codes and took the drive to work and I got this...
https://drive.google.com/open?id=0B7...EZiN1VzeEdQcW8

The under load LTFT actually got up to 4.7 and rising. Trying to figure out if the O2 is bad or is it possible to have a lean condition only under load. I'll probably do the Carb Cleaner test on the vacuum hoses later.

[old guy]

I think you are confusing your LTFT and STFT. The LTFT should eventually stabilize and remain the same whether you are driving or at idle. Think of your LTFT as your base map adjustment. The STFT is going to constantly change. Once you reset your ECM both trims will go to zero. You will see a lot of activity on the STFT and a gradual change in the LTFT until it reaches the required state for the ECM to maintain the proper A/F ratio.

According to Audi/VW a LTFT range of ±10° is considered acceptable. Some reasons for a high additive with the LTFT could be a dirty or defective MAF sensor or a chronic false air condition allowing non-metered air into the intake. Check for cracks or splits in your block breather hoses. Last year I noticed an increase in my LTFT and it was a cracked PCV elbow coming out of the lower block breather.

[mosnet99]

I think you are confusing your LTFT and STFT. The LTFT should eventually stabilize and remain the same whether you are driving or at idle. Think of your LTFT as your base map adjustment. The STFT is going to constantly change. Once you reset your ECM both trims will go to zero. You will see a lot of activity on the STFT and a gradual change in the LTFT until it reaches the required state for the ECM to maintain the proper A/F ratio.

According to Audi/VW a LTFT range of ±10° is considered acceptable. Some reasons for a high additive with the LTFT could be a dirty or defective MAF sensor or a chronic false air condition allowing non-metered air into the intake. Check for cracks or splits in your block breather hoses. Last year I noticed an increase in my LTFT and it was a cracked PCV elbow coming out of the lower block breather.

No I understand the LTFT, and it was stable (at 6.2%) before I cleared the codes. The trip was only 15 mins and it kept rising past 4.7% probably because it was trying to get back to the 6.2% base for the additive. I'm thinking its my MAF too.

[old guy]

Understood. I misinterpreted this comment. I now assume you meant the STFT was around .8%. The LTFT wouldn’t change like that between idle and driving.

Okay so The LTFT under load when I started was 6.2 (a bit high) but the idle LTFT was on spec at .8.

[mosnet99]

Understood. I misinterpreted this comment. I now assume you meant the STFT was around .8%. The LTFT wouldn’t change like that between idle and driving.

Well the idle and under load LTFT starts at 0% right. But if the STFT is reading a rich condition and your at idle then the idle LTFT will begin to make a new base idle trim. This was the .8 I was speaking of that I started with before I cleared the codes. After I cleared them and idled for a few mins the new base idle was 1.1%. Does that make any sense? Maybe my understanding is flawed

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[old guy]

Sounds like you have it right. I was referring to the adaptive (partial) LTFT and you were referring the the adaptive (idle) LTFT.

If at idle the STFT constantly adds fuel the idle LTFT will eventually increase until the STFT will not have to continue to add and starts to bounce back and forth around 0%.

Once you start driving the same thing happens to the adaptive partial LTFT.

[old guy]

If you have an hour to kill watch part 1 and part 2 of these videos. It is one of the best down to earth explanations of fuel trims and how to use them for troubleshooting engine performance issues that I have ever come across. If you are just learning about fuel trims I think you will find it time well spent.

[mosnet99]

If you have an hour to kill watch part 1 and part 2 of these videos. It is one of the best down to earth explanations of fuel trims and how to use them for troubleshooting engine performance issues that I have ever come across. If you are just learning about fuel trims I think you will find it time well spent.

I will. Thanx OG

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[mosnet99]

Pretty sure it's the MAF now. Today my acceleration was all over the place like the car had no idea how much metered air was coming in. Then it would come back & drive normal. I have an OEM maf on the way. Thanx everyone

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