Running Rough issues mk4 GTI AGU

[panjo42]

So recently my mk4 GTI (AGU) started to miss badly. We narrowed it down to cylinder 3 missing, and searching the forums I found that it was likely a bad ignition amp. To be safe though we testing injectors and did a compression test as well. Injectors worked fine and compression was great, 180 across all 4. We changed spark plugs for good measure as well.

So I ordered a new ignition amp and new coil packs because we had replaced one earlier in the year and I thought getting 4 fresh new ones would be a good idea.

Once I got the new ignition amp on, it's started immediately running perfectly. However, after about 2 days (30km of driving) it started to run really rough. Shaking and struggling from about 2-3k and then just slowly accelerating after that. Also I can't feel any turbo.

While testing a few things, including cleaning the maf, I ran the car for bit with the maf unplugged accidentally, however this didn't change the feel at all. This leads me to believe that the maf is the issue here. I just wanted to double check any other possible issues though, as sourcing a MAF to Australia isn't cheap easy and quick.

Thanks

[sambb]

Usually if the MAF is bad and you unplug it, the car will then run better. Is your N75 plugged in/not open circuited wiring/solenoid operating correctly? Anything wrong there and the turbo could just just be on spring pressure which is about 5-6psi which might explain the boost issue. Definitely no vacuum leaks? eg anything post-MAF eg, diverter valve plumbing, IC hoses, PCV system/hoses including the crankcase breather fitting, PRV, badly cracked dipstick etc Leaks will play havock with your mixtures.

[panjo42]

Other than just seeing if it's plugged correctly, what's the best way to test the n75?

[panjo42]

Update:
Voltage checked the maf sensor plug. Not getting anything. That would explain why there was no change driving with and without it plugged in.

[sambb]

0v on the n75 you should be able to blow from signal side to wastegate line. 12v you should be able to blow signal side to TIP side. That's only part of the story as it has to pulse with a duty cycle but that test will at least expose whether or not its jammed one way or half way. resiatnce check the coil also to make sure its neither open circuit or shorted.
Good find on the MAF. Hopefully not a nightmare to find the source of the problem.

[panjo42]

Where should I start looking Re: the maf. Why would the plug not be getting power?

The n75 was getting 12v

[panjo42]

Update:

The fuse #43 isn't getting power either. It's showing the same 0.04 volts as I was getting with the maf sensor plug.

[h100vw]

.04 volts isn't anything. That's probably as close to ground as your meter will go.

The fuse was blown? Coilpacks on the mk4 GTI are pretty serviceable but with time marching on, it's probably not a bad move replacing them. Keep a good one in the glovebox.

[panjo42]

I just replaced the coil packs. And the fuse wasn't blown, the fuse wasn't even receiving any power. (Tested with the multimeter)

[No457 Snowy]

You might be able to pick up an MAF from here: Mass Air Flow Sensor - Euro Revolution
There's a mobile number on the site you could call (used to be Seb or Courtney, members here, not sure if that's still the case).

If you get stuck maybe take it out to Canberra VW Centre in Belconen, great guys there, they'll get it sorted quickly.

Edit: sorry I didn't realise this thread was a few months old.....