I have a 2001 TT with a Garrett chip and ECS diverter valve among other small mods. I can't figure out what's causing a sputter at 4200 rpm's and above. Has anyone else experienced this? It was first diagnosed as bad ignition coils, replaced those to no avail... then a vacuum hose, again replaced with no change. The problem seems to be getting worse. Any ideas?
Thanks!

 

do you have cold range plugs gapped to 0.028?

 

^ i would go with no on that one

spark plug info is in the FAQ on top of this forum

 

Found your problem...

Have you gotten a check engine or EPC light yet?

 

I 'd go for that as well. When this happened to me, a simple change in the plugs did me well and cleared the issue.