Hello every one,

 

My octavia BFQ engine, when cold runs rough and sometimes during the movement but not always.

 

When it runs rough the brakes don't work properly, probably low air pressure.

 

I have the warning light P0171 and P0131.

 

I have cleaned the EGR Valve, runs ok. Changed the sparks and sparks wire, replaced air hoses.

 

But still nothing seems to worked.

 

Could the 02 sensor cause this ?

 

It's a costly sensor and wouldn't want to buy it without reason.

 

At the repair shops said its not the 02 sensor causing this but probably something in the engine but i doubt, if it was a broken engine the problem would be permanent.

 

It must be a sensor ?

An air leak is the first thought on something like this, but other possible issues could include a pre-sensor exhaust leak, faulty fuel delivery, wiring problems, air flow sensor and O2 sensor. You should note down the freeze frame data.

 

Do you have a scan tool that can graph one or more live data PIDs? If you do, you should do some simple tests while monitoring both fuel trims (STFT & LTFT) and both O2 sensors. Tests should be done when the engine is at operating temperature.

 

Test 1: Running at idle. Note both fuel trim values once they've settled off. Monitor the voltage of the B1S1 O2 sensor, it should hang around 1.4  - 1.6volts. B1S2 O2 sensor should hover between 0.2 and 0.8 volts. Run like this for a while and observe anything that happens.

 

Test 2: Running at increasing RPM. Run at, for example 2000 and 3000 for a while. Measure and note the same values.

 

Test 3: Rapid WOT and release, do this a few times, waiting some moments between each one for the readings to settle. Make a mental or written note of what exactly happens to the B1S1 O2 sensor and STFT.

 

Regards.

15 minutes ago, LightRain said:

An air leak is the first thought on something like this, but other possible issues could include a pre-sensor exhaust leak, faulty fuel delivery, wiring problems, air flow sensor and O2 sensor. You should note down the freeze frame data.

 

Do you have a scan tool that can graph one or more live data PIDs? If you do, you should do some simple tests while monitoring both fuel trims (STFT & LTFT) and both O2 sensors. Tests should be done when the engine is at operating temperature.

 

Test 1: Running at idle. Note both fuel trim values once they've settled off. Monitor the voltage of the B1S1 O2 sensor, it should hang around 1.4  - 1.6volts. B1S2 O2 sensor should hover between 0.2 and 0.8 volts. Run like this for a while and observe anything that happens.

 

Test 2: Running at increasing RPM. Run at, for example 2000 and 3000 for a while. Measure and note the same values.

 

Test 3: Rapid WOT and release, do this a few times, waiting some moments between each one for the readings to settle. Make a mental or written note of what exactly happens to the B1S1 O2 sensor and STFT.

 

Regards.

Hello,

 

Thanks for your reply.

 

I have a simple BT OBD, can i do it with this one ?

 

They checked for air leak with smoke, they didnt find anything, and if it was an air leak, would have rought running all the time ?

 

Oh forgot sometimes when it runs rought, i switch off the engine and on again (switch on roughly) and problem disappears !

Air leaks tend to get better at higher speeds due to the lack of vacuum when the throttle butterfly is opened. Huge gaping holes in the air system are a different matter, but you'd usually see or hear them anyway. But, air leaks can be counted out. I guess an exhaust leak can also be counted out, if you had one that far up in the system you would hear it.

 

I don't know the capabilities of your OBD tool (what's its name?), I guess it runs off of a smart phone? If it has live data ability then you can monitor things with it. It should most certainly store freeze frame data of the reported fault codes. Graphing is preferred, but if you don't have that but can still view live data as just numbers then that will be fine for this. It'll just require a little more concentration.

10 minutes ago, LightRain said:

Air leaks tend to get better at higher speeds due to the lack of vacuum when the throttle butterfly is opened. Huge gaping holes in the air system are a different matter, but you'd usually see or hear them anyway. But, air leaks can be counted out. I guess an exhaust leak can also be counted out, if you had one that far up in the system you would hear it.

 

I don't know the capabilities of your OBD tool (what's its name?), I guess it runs off of a smart phone? If it has live data ability then you can monitor things with it. It should most certainly store freeze frame data of the reported fault codes. Graphing is preferred, but if you don't have that but can still view live data as just numbers then that will be fine for this. It'll just require a little more concentration.

So you believe should be air leak ?

Its an elm connection with smartphone, have torque pro ill see if has live data rec

Also it burns a bit oil about half liter per 800km. Another repair shop said its cause of that. But without having much knowledge those 2 things seems total different. Air pressure and rought idle cause of oil burning ? doubtful

No, I first thought that, but you said it was tested. Sorry, I said "air leaks can be counted out", meaning, it is probably not an air leak.

 

Torque is a popular system I think, so I guess it has what is required. It may even have graphing. This just makes it a lot easier to be aware of what is happening. Looking at numbers updating in a list, especially on the snap throttle test, is very difficult.

 

Oil consumption could be excessive and that could lead to a bad idle, but, if the lambda control is working fine then this should be accounted for in fuel trimming. I don't know if your consumption is excessive for this engine.

2 minutes ago, LightRain said:

No, I first thought that, but you said it was tested. Sorry, I said "air leaks can be counted out", meaning, it is probably not an air leak.

 

Torque is a popular system I think, so I guess it has what is required. It may even have graphing. This just makes it a lot easier to be aware of what is happening. Looking at numbers updating in a list, especially on the snap throttle test, is very difficult.

 

Oil consumption could be excessive and that could lead to a bad idle, but, if the lambda control is working fine then this should be accounted for in fuel trimming. I don't know if your consumption is excessive for this engine.

It's excessive i think, but gas consumption is within limits so it's not in that bad state.

 

What else you think can be ? because the problem is not permanent and it only happens mainly when cold

OK then.

I couldn't tell you what I think it is with any certainty yet. I'm now wanting you to run tests to verify the condition of the pre-cat O2 sensor. Basically, if the O2 is feeding incorrect data to the computer, the computer will adjust fuelling to fit with that data. Or the O2 is so badly malfunctioning the ECU is not letting it control the fuelling and operating using stored mapping.

This car has a wideband O2, they're really hard to diagnose with 100% certainty without VAG equipment. But, by following a "belt and braces" approach, enough information can be gathered to make a reasonably certain call.

 

But anyway, tests are easy to do, you don't even need to get out of the car or open the bonnet. So they're the best place to start

8 minutes ago, LightRain said:

OK then.

I couldn't tell you what I think it is with any certainty yet. I'm now wanting you to run tests to verify the condition of the pre-cat O2 sensor. Basically, if the O2 is feeding incorrect data to the computer, the computer will adjust fuelling to fit with that data. Or the O2 is so badly malfunctioning the ECU is not letting it control the fuelling and operating using stored mapping.

This car has a wideband O2, they're really hard to diagnose with 100% certainty without VAG equipment. But, by following a "belt and braces" approach, enough information can be gathered to make a reasonably certain call.

 

But anyway, tests are easy to do, you don't even need to get out of the car or open the bonnet. So they're the best place to start

ok ill run the tests.

 

So, 02 sensor can cause this ? pre cat one ?

It could, but I'm not saying it is. Let me know what you find and we'll go from there.

02 sensor bank 2 runs 0.2-0.7 but sensor bank 1 runs at about 0.9-1 and sometimes i don't get any reading at all.

If that is the voltage reading for B1S1 then that looks interesting. It looks a lot like the equivalence ratio reading of a good sensor. Are you sure you measured volts?

Didn't you manage to find short term fuel trim (STFT) and long term fuel trim (LTFT)?

 

It would be better if you could run the tests I mentioned in my first post, here they are again:

 

Test 1: Idle. Note both STFT and LTFT values once they've settled down. Note the voltage of the B1S1 O2 sensor, it should hang around 1.4  - 1.6 volts. Note the voltage of the B1S2 O2 sensor, it should change between 0.2 and 0.8 volts. Run like this until everything seems stable.

 

Test 2: Running at about 2000 RPM first then about 3000 RPM for a short time. Note the same values at 2000 and 3000 as you did for the idle test once things have settled down.

 

Test 3: Rapid full throttle and immediate release (called a snap throttle test). Do this 2 or 3 times, waiting some moments between each one for the measurements to settle. You will need to display a graph of what exactly happens to the B1S1 O2 sensor because there is a certain pattern I am looking for. 

 

Anyway, good night.

Hello members!

 

From a few days on my '06 MK 1 Octavia,  1.6 petrol, BFQ engine I noticed a strange thing, which I don't know if it is normal or not: if I am revving up on idle to 2000 or more rpm, I am letting go to the throttle, the rpm is dropping with a certain speed, but from 1500 rpm this dropping speed is slowing down, untill it reaches the idle rpm. I have no MIL, scanned I am having periodically only the 16555 error, with lean mixture, intermittent. I will attach a short movie about this to be more clear.

 

What I or my mechanics did before:

- S1 B1 oxygen sensor was changed 3 months ago, because I had an error regarding to this,

- the intake manifold was cleaned,

- also the TB, which was adapted also by me with the Vag-com,

- the valve cover gasket was changed because of oil leaks.

- air and fuel filter was changed also 3 months ago to a high quality ones.

 

Once also happened, that I was revving untill 1000 rpm, the rpm dropped, and the engine stopped.

Also, when the engine is cold, sometimes, the rpm is remaining around 2000 for a few seconds, but only with the cold engine. When it is warm, I have the situation described at the begining.

 

Do you have any idea, this rpm dropping speed slowing down is normal? I guess not, because like I wrote, I have periodically the lean error, and not only.

What is your suggestion, what should I check?

 

Thank you.