MKIV GTI has developed a miss

[dubbed]

Hey guys just a quick update because I'm buggered..

A very big thanks to Marshall (user name kept private unless he wants to say) who was kind enough to spare his time and scan my car for errors with a VAG-COM. There were a couple of errors but the one that is the culprit is '00575 - Intake manifold Pressure 08-10 Control Limit Surpassed - Intermittent'.

I did a quick search on Google and I've narrowed it down to: split/loose hose, N75 valve, MAP/MAF? sensor, and the worst case scenario; VNT jamming/a busted turbo. What are people's thoughts? I will get it down to a service centre but it's difficult working six days a week so if it's something easy I'd like to have a look myself late tomorrow or Sunday.

Thanks again to everyone's help so far

[h100vw]

You don't have a VNT turbo on that one mate, they are on diesels.

What's happened is that the ECU has sensed an excessive boost condition and is protecting your motor.

Have a read up on testing wastegates on google as I haven't ever had to. Probably just blow or suck on the hose connection and make sure it opens up.

The N75 should be easy to test too.

Did you have that code cleared out?? It should run ok for a while until you cause the problem again by running it hard.

Good job you didn't buy any coilpacks.

[dubbed]

Ahh well that's a relief. I'm still getting used to all the turbo terms and gadgets.

Yes the code was cleared out but it didn't change the running of the car. If anything it's gradually getting worse (I only drove it to get the codes checked and then straight home). When I started it up last it sat there idling smoothly for a little while and then suddenly idled like a truck for half a minute and then repeats. I don't know where the wastegate is but noticed I have a GFB something-or-other. I think it's a plumbed-back BOV...

I also noticed my temp gauge has changed after the VAGCOM. It used to sit dead on the centre, now it's one bar below. Where should it sit at optimum operating temperature?

And yes, thanks to you guys I'm very lucky I didn't go out on a hunch and buy new coils haha. The VW stealer wanted 90 pingers just for one!

Thanks for your help h100vw

[h100vw]

I would have a look at your GFB plumbback dv and make sure it's working OK.

If it's not releasing the pressure in the intake when you lift off, maybe that is causing the code??

Gavin

[sierra055]

The GFB does sound like it might be a DV, is it at the rear of the engine bay, passendger side? Personally I don't think that it would be causing the symptoms your car shows, nor would the N75 valve. The valve is also located in that back left corner, right next to the DV.

Below is a pic of the DV and N75 valve.

My thinking is that it is a faulty MAF. You should be able to test it by disconnecting the MAF. If it runs better, there's your culprit.

[dubbed]

Yeah must be a DV. Aren't they virtually the same thing?

I might try disconnect the MAF and see what happens...

[dubbed]

I unplugged the MAF but it didn't seem to make a difference. It's running rich because I can smell petrol but I don't know if it's related to the MAF being disconnected..

[h100vw]

You can disconnect the MAF but that's not always going to prove the MAF to be faulty. My mates A4 with APU motor, seemed to run OK somedays and not others. Disconnecting the MAF made no perceptible difference. It wasn't 'til I chipped it for him that we could see for sure that it was dieing. It was only failing big time when under boost.

We had previously logged the airflow and even that looked to be good.

If you can get back on the VAG-COM and do a couple of runs in 3rd gear from 2000 revs to the redline while logging the airflow, that would be a good test of the MAF.

There is a formula on ross-techs site that tells you how to convert Airflow to hp. I reckon it could be divide by .8. ie for a std AGU you would get around 120g/s.

On the Audi you could see the airflow drop to zero intermittently while under boost, completely giving the game away.

If you could borrow a MAF from another good car, I'd try that over disconnecting.

Gavin

[shami]

I had a similar issue with my mk4, found out it eventually that it was the MAF...it seemed that the old one didnt exactly die...but didnt exactly work...if that remotely makes sense.

But the symptoms you describe are very much similar to what i had.

[dubbed]

We had previously logged the airflow and even that looked to be good.

If you can get back on the VAG-COM and do a couple of runs in 3rd gear from 2000 revs to the redline while logging the airflow, that would be a good test of the MAF.

There is a formula on ross-techs site that tells you how to convert Airflow to hp. I reckon it could be divide by .8. ie for a std AGU you would get around 120g/s.

On the Audi you could see the airflow drop to zero intermittently while under boost, completely giving the game away.

If you could borrow a MAF from another good car, I'd try that over disconnecting.

Gavin

Quick update. I was lucky enough to have use of the VAG-COM again and logged some data this time (thanks Marshall). Of course tonight when I drove the Golf it barely missed a beat; it actually ran better than it has for a while.

First up VAG-COM showed us an error specifically with the MAF different to the faults I posted up earlier. Also bear in mind that the codes were cleared after scanning the first time. I forgot what the fault was exactly but it had something to do with a signal from the MAF that was too low/intermittent.

Below is a back-to-back comparison of my Golf (the blue table) and a normal running MKIV GTI. The blue table was not done under load (i.e. just blipped the throttle a few times whilst stationary) whilst the red table had some WOT action.




Okay so we've concluded the MAF on mine is buggered and getting false/bad readings for some reason, but we're not mechanics . Could it be as simple as dirty sensors in the MAF? I was considering giving it a squirt with carby cleaner or something.

Car will be serviced in the coming week.

[h100vw]

Assuming both runs were done with full throttle, there is something amiss with yours.

To do a decent log you need to have it pull up a hill in 3rd (4th is better but you'd be locked up most likely) from 2000 revs to the redline is possible. The steeper the hill the better, the engine won't accelerate so quick and you get decent info in the logs cos the parameters aren't changing at lightspeed.

What about swapping MAFs with Marshall and doing a run? Depends how much you can get a replacement for.

Jmac has one that belongs to me, it's brand new. Let me have the part number. You can try it for the cost of postage.

Gavin

[dubbed]

Geeze mate you don't muck around Love it!

We didn't end up swapping MAFs because my car was behaving as normal and I didn't want to take up his whole evening.

Gavin that's a fantastic offer!! How much do they retail for? MJM Autohaus and German Auto Parts sell them for about US$180. I will get you a part number and PM you.

I must say you Dubbers are a seriously friendly and helpful bunch! Thanks so much for the help and the new found knowledge along the way

[h100vw]

I know how much of an arse it is, doing the running around to find bits. You would be surprised that Imparts were with a handful of dollars more than I paid to get this one over from the UK.

037 906 461 C is the part number for the one I got.













Oh and if I am nice to you, you might have your car chipped....

[goodfella]

I also have a spare MAF, brand spanker Bosch, but its sitting in my car boot, and I am cozy inside so I'll post the part no tomorrow.

[dubbed]

Hey chaps. Just a quick update.

The car was running fine for a while but would still occassionally feel like it's missing/loss of power/idle like a truck. I finally found time (well, I found someone else with the time!) to take my car to VolksPower to get a new MAF. Dean was a bit funny about replacing the MAF saying it could be anything even though their report brought up a MAF error. Well he replaced it anyway and the car is running like a champ

It cost approx. $250 for the MAF and $40 for labour. A bit exxy so I just hope it doesn't eff up any time soon. Will be interesting to see the VagCom diagnostics now...