Repair-It

Is it something you notice under conditions other than WOT (or near WOT)?

No, not that I can think of, except maybe a rough idle randomly. It is weird. The car is usually really good except for these things that don't happen often.

So you don't have a fuel filter and we can't check the fuel pressure? That makes this difficult.

What else is "difficult" is that apparently there is a cutout under the seat where the fuel pump is in the tank, but people say that it isn't big enough for the pump to fit through so the whole tank has to come off... That is something I don't really want to do unless it is absolutely necessary, and would likely be better to do in the spring.

Oh wow.

Most of my vehicles have required the tank to be removed so I guess I am used to it. It's not too bad if you can run the tank really low first.

Lucky for me my CTS-V got a brand new fuel pump assembly under that recall a few years back.

bill25 wrote:I found one. This is one of the cheaper ones. I didn't realize these were so expensive.

https://www.ebay.com/itm/Original-2009- ... SwutpZlHFu

I might order this to start:
https://www.amazon.com/Haynes-Repair-Ma ... da+Mazda+3

I understand that this will probably not have the same level of detail. If my car were more interesting I would probably want the Shop Service Manual.

~$150 is what most "late model" FSMs cost used. You can find older stuff for <$100. Some new stuff might only be available electronically ("new" being since 2010).

At least these guys have free wiring diagrams and TSBs:
http://www.bbbind.com/free_tsb.html

I just checked.

Wonder if this has anything to do with the situation: 01-007/09

http://www.bbbind.com/free_tsb.html

There is a TSB for instability of idle when stopping - That is my bad idle complaint. Car has rough idle just after a stop. Almost stalled on me a couple times...

Basically says to clean the throttle body, because carbon deposits could lead to decreased airflow. This could also have something to do with the WOT issue also...

That is probably your idle issue. It's funny because I just cleaned the TB on my STS.

Unfortunately that won't do anything about your power issue. The decreased airflow refers to when the throttle is nearly closed (at idle). It won't change the airflow when it is open.

Decent video for reference:
https://www.youtube.com/watch?v=75I24szhsco
Better:
https://www.youtube.com/watch?v=MhlWnPk5DqI

That dirty TB issue may be your starting issue.