So, there’s a thing called the ‘stumble’, where there’s a fueling issue that causes an STI engine to falter or lean-out. In some cases, it is noticeable, especially when getting tuned. Some tuners can tune it out while other can’t/won’t.
There are several fixes: 1) using an aftermarket fuel pressure regulator; 2) using an aftermarket fuel rail; 3) extending a fuel line. The below links describe how to perform #3. As well, after doing fix #3, it is advised to use Cobb’s Accesstuner (if you don’t have it, you can request it from Cobb at this link) to modify your TGV tables (as they were modified by Cobb to compensate for the stumble)…the first URL below explains how to do it.
I do plan to do this as soon as I can. It shouldn’t take any more than 20 minutes and shouldn’t cost any more than $20 in material. I plan to do this before I get protuned.
Note that this only affects later model STIs (2008-2014)…it does not affect the WRX or other models.