Long post, but it kind of needs to be.
Have you ever felt really, truly stupid?
I have been plagued by codes and CELs since I bought the car, mostly 1175s and related. The oil, when changed, has smelled like gas to high heaven. I did the intake manifold and all associated gaskets, but still had issues, although fewer in number.
So, I decide to change the last gasket on my engine's top end: the secondary throttle body gasket.
So I buy the part, and go to install it last weekend. It doesn't fit. In fact, there's an O-ring acting as a seal. I can't figure things out, so I decide to check the boot from the MAF to the secondary throttle body and see if it goes there. No dice. But what do I see on the secondary throttle body? A groove for an O-ring, similar to the one between the two throttle bodies. No O-ring, but the groove is there.
So, I check a couple of websites and discover that in fact there is supposed to be a rubber ring there to seal the boot to the secondary throttle body. As well, there is supposed to be a ring to seal the MAF to the boot.
I have had that boot off a few times now. Since I bought the car there has never been a rubber ring in either spot. Never.
All of these issues, all of this time, all of this anger at the car, and it was a couple of rubber rings that should have been there, but weren't.
All I can say to this is

Effing hell!