Don't have to pull the TB to clean it, just long fingers. Be sure power off and unplug it first and careful of the gears when moving the butterfly.
Shouldn't need a new gasket, it is an O-ring.

 

 

Yeah, I tracked down some horror stories on here about others removing the TB to clean it.

IE
https://www.chevyhhr.net/forums/prob...g-49401/page6/

 

I have been following this thread with great interest since my wife's HHR (2010 2.2l) is behaving similarly and I too have been going over the same stuff you have with the same unhappy results. However I had a Ha-ha moment last night. All along I have been comparing this to the old automatic choke not working on cars from the past. Somewhere in this post you folks discussed the engine temperature sensor and it got me to thinking so yesterday after driving I set the DIC to show the engine temp once the key was turned to on. This morning I turn the key and noted the temp read 90C (194F). Pretty warm for a car that hasn't been run for 8 hours and has been sitting in -5c (29F) weather all night. As I drove the car the temp dropped to a lower temp that was more believable and rose steadily as it warmed up.

I'm going to keep an eye on the temp reading when the engine is dead cold and ask you to do the same for a couple of day's. I'm suspecting that the ECM is getting incorrect info and therefor not adjusting the fuel correctly for these cold starts.
Although I would think that it would be a lean condition not rich but at this moment??? I'll try anything.

 

If you had a scanner that you could see Short Term Fuel Trim (STFT) values if might lead you to your cold start problem.
Here's something to read:
https://www.obd-codes.com/faq/fuel-trims.php

 

I checked mine in the video. It showed 48 degrees when it was 30 degrees out. I actually purchased a new AC delco one just in case.
I'm going to confirm with a proper scanner this weekend.

 

Fuel trim system rich (p0172) does not mean the engine is running rich!! It means that the ECM is adding fuel to the A/F. For some reason they don't teach reading entire sentences in auto trade school, 99.9% of ASE certified mechanics will do the same thing. The descriptor is not "fuel system rich" it is "fuel trim system rich".

 

Okay, and the difference is?

***EDIT***
I read Cat Man HHR link about Long and Short Term fuel trims and what I took away from that is Lean is rich and Rich is lean.

Still confused about the difference between fuel system and fuel trim. It's early and I'm groggy from meds so... I'm gonna go do a search cause I suspect fuel trims are part of the fuel system and I need to know the who, what, how and why of it. A no know the lingo issue on my part.

 

From #137

 

You want to focus on short term, that is what is happening now in real time. Just like Don is saying, when % shows high that means the system has a vacuum leak and the ECM is commanding for more fuel to compensate to get it back to 0%. A minus % is just the opposite.


The first part of this video up to 1:24 will help you understand Trim. The rest is good brain food.