Why do you thijnk replacing the throttle body will cure it?
Is the CEL on, what codes ?

 

 

 

 

Is it an SS ?
If it's a LS or LT (2.2 or 2.4) replacing the throttle body isn't hard to do.
For the P2135 code you have to buy the complete throttle body. After installing you have to do a relearn on the idle. Looking at some videos shows if you have a quality scanner you can do it yourself otherwise a dealer or good repair shop can do it for you.
I would have the codes looked at with a quality scanner (not Autozone) for how many times each one did happened.

 

As Cat Man stated, you need to confirm which HHR you have. There is a big difference between the regular LS, LT's and the SS turbo engines.

 

I think the difference comes when R&I of throttle body. 2.2 and 2.4 are easier to do.
Rockauto shows the 2.0 and 2.2 take the same part number for the throttle body, 2.4 is different.

 

 

What model is it ?
Look at the sticker on the glove box door.
From what I've found code L61 is a 2.2 and LE5 is the 2.4.
I myself never looked but under the hood should be an emission label with the size on it.
Also by your questions I would have a repair shop do the work.
Just my 2 cents.