Constant MAF issues!!!

[AndyNF]

Hello all. I’ve been getting advice from this site for a while, but I’m still struggling to pinpoint why every few months my 2010 superb 1.8tsi goes into limp mode with the p0101 code. I have changed the sensors (Bosch official) cleaned them, had the wiring investigated, and in between it always works great, but for only 3 or 4 months then it all starts again! Has anyone else had this? I’m left wondering if the root cause lies somewhere else and I’m not dealing with the real issue. My next port of call is to go to Skoda for investigation, but that’s going to be expensive. Has anyone dealt with them, especially in the Southampton area? I love the car, but this issue is a real headache. 

[J.R.]

Are you 100% certain that nobody perhaps under previous ownership has mucked around trying to disable the EGR system, most likely with a blanking plate with a metered hole to pass some air to fool the ECU.

[AndyNF]

I wouldn’t have a clue to be honest. Would an EGR fault come under the same code as MAF? I have suspected the EGR before ( sticky valve maybe)  but it’s always been another fix to get it going again. 

[AndyNF]

UPDATE - I left the car idling in the driveway for maybe 10 minutes this morning. To begin with it ran a bit rough and was under revving. When I applied throttle it would flatline at 2000 with a really slow pick up afterwards, which I guess is the limp mode kicking in. Then it started to pick up and was steady, throttle started behaving normally and was fine on a road test. So whatever it is it’s intermittent. I just wish I knew what it was 😂

[J.R.]

28 minutes ago, AndyNF said:

I have suspected the EGR before ( sticky valve maybe)  but it’s always been another fix to get it going again. 

 

That is your answer then IMO.

 

To explain how the faults are related, the signal from the MAF sensor to the ECU must be within a certain range according to the conditions reported by all the other sensors or it will be considered implausible.

 

Consider the engine running at a constant 3K rpm and with a fixed throttle opening, the airflow is expected to be X +/- 5% for example, when EGR is commanded this airflow should fall by for example 8% because the engine is now getting 8% of the intake charge from EGR gases (all these figures are made up and are probably way out), the ECU will expect to see the airflow reported from the MAF drop by 8%.

 

If the EGR mechanism is blocked or a blanking plate is used then the airflow will not drop and the ECU will consider the unchanged value to be implausible, the error code is for the MAF but it could equally be an airleak elsewhere or in this case little or no EGR gases passing.

 

The EGR mechanism should have a sensor showing the opening angle and that should be the first fault code if it is sticking as the measured angle would differ from the commanded, there are various bodges to overcome this and I suspect your car has had one or maybe that version of the EGR lacks the feedback.

 

You do not need to replace the EGR, you could fit an Emulator/simulator as I have together with a blanking plate, what it does is to modify the output from the MAF when EGR is commanded to fool the ECU that the airflow through the MAF has dropped by the required amount. This is why I have an understanding of the subject, I wont fit anything claiming to do something without understanding the how and why.

 

They cost about £99 from a Polish Ebay seller.

[AndyNF]

Thanks J.R! I think this has to be my next port of call. I’ve replaced everything else and a smoke test didn’t show any leaks. 

[Krahvi]

That what happend to me. EGR needs to be correctly written out of ecu. 

[andrehj]

On 31/07/2023 at 13:06, AndyNF said:

I wouldn’t have a clue to be honest. Would an EGR fault come under the same code as MAF? I have suspected the EGR before ( sticky valve maybe)  but it’s always been another fix to get it going again. 

The 1.8 TSI doesn't have an EGR valve, so you can rule out that one. (EGR is performed by valve overlap).

[andrehj]

On 31/07/2023 at 13:47, J.R. said:

If the EGR mechanism is blocked or a blanking plate is used then the airflow will not drop and the ECU will consider the unchanged value to be implausible, the error code is for the MAF but it could equally be an airleak elsewhere or in this case little or no EGR gases passing.

 

The EGR mechanism should have a sensor showing the opening angle and that should be the first fault code if it is sticking as the measured angle would differ from the commanded, there are various bodges to overcome this and I suspect your car has had one or maybe that version of the EGR lacks the feedback.

This advice is useless. Please learn how the EGR of an 1.8 TSI works before giving wrong advice...

[Crasher]

@AndyNF What is the VIN?

Edited 1 August, 2023 by Crasher

[J.R.]

3 hours ago, andrehj said:

This advice is useless. Please learn how the EGR of an 1.8 TSI works before giving wrong advice...

 

Thankyou for your kind words, would you care to enlighten me?

[AndyNF]

I’ll grab the VIN later as the car isn’t nearby atm…

[andrehj]

On 01/08/2023 at 21:27, J.R. said:

Thankyou for your kind words, would you care to enlighten me?

I already did that in the previous post (valve overlap). The inlet camshaft has a hydraulically operated adjuster. By changing this adjuster, the inlet valve opens earlier, during the last part of the exhaust phase. In this way part of the exhaust gasses are blown into the inlet, and reused.

[AndyNF]

Sorry it took so long! Here’s the VIN TMBKB7315B9050778. Cars driving fine ATM but it’ll go limp again in a few weeks. That’s why I wondered about a stick EGR. 

[J.R.]

54 minutes ago, andrehj said:

I already did that in the previous post (valve overlap). The inlet camshaft has a hydraulically operated adjuster. By changing this adjuster, the inlet valve opens earlier, during the last part of the exhaust phase. In this way part of the exhaust gasses are blown into the inlet, and reused.

 

Thats what I used to do on race engines for scavenging but it worked in the direct opposite fashion of what you describe, the overlap period allowed the inertia of the outgoing cooling exhaust gases to create a pressure drop in the cylinder expelling the exhaust gases drawing in fresh mixture improving the volumetric efficiency.

 

Are you sure that you dont mean the inlet valve opens later  and/or exhaust valve closes earlier with no valve overlap and scavenging to retain residual combustion gases?

 

I cant see how exhaust gases can be blown anywhere but out of the cylinder, when you say blown into the inlet do you mean the inlet manifold?

 

 

Edited 3 August, 2023 by J.R.