APRTT225

So here it goes...

I've been having an ongoing misfire issues for about 2 months now. It's an 02 TT 225 Quattro, 103K miles, APR stage 1 (had for over 2 years), Forge 007 DV, Neuspeed intake and Milltek exhaust.

The problem seemed to start about a week after I got the crank sensor replaced for random stalls. At that time I also replaced the spark plugs (Denso Iridium) and fuel filter. Misfire started off minor but progressively got worse to the point I could barely rev beyound 3k RPM without it misfiring. For the longest time it wouldn't even pull a code until one day it pulled a P0172, misfire detected cylinder 2. When this happened the check engine light flashed for 10 seconds, shortly after it started staying on permanantly. To make a long story short, here's what I've done so far:

1. Replaced N75 valve, no change
2. Replaced coilpack, no change
3. Swapped fuel injector with different cyclinder. Reset code, came back to cylinder 2.
4. Performed boost leak test. Found a couple leaks, replaced hosing and PCV valve. Helped a little but still misfiring.
5. Smoke tested vacuum system and didn't see any smoke coming from anywhere. Even tried using the carb cleaner around the intake manifold at idle but no changes in idle.


The latest thing I have done is after a friend told me the Denso Iridium plugs made his Supra pushing 25psi misfire like crazy, I decided to change them out with OEM dual platinum plugs gapped to .028. This made the misfire a lot less severe and code has gone away, but misfire is still occurring. It's hard to explain exactly what it's doing, but basically:

- Idle is completely normal and not erratic at all.
- Boost comes up normal most of the time but starts to misfire at top end, then I'll change gears and the boost is REALLY slow to come up, sometimes only boosting to 5psi which I believe is limp mode (also, no check engine light or code being thrown).
- Sometimes, boost is VERY slow to come up, then as soon as it gets to 7-10 psi, it seems like a valve or something opens and boost shoots to 20ish psi and will then misfire like crazy. However, the check engine light is not flashing like it used to when it misfired. So it's really hard to say if it's a boost issue or engine misfire issue.

I'm going to try to get a video posted soon so you can better see what I'm talking about.

Anybody have any ideas as to what my next step should be? What am I missing?

systdow666

Sorry i know this is an old thread but have you checked your fuel pressure this sounds like a fuel starvation issue especially since it comes on with boost