just got another HHR. 2007 2.4 with about 161K. overall is in very good condition compared to most i've come across. Seems like previous owner must've cared about the car for the most part.
Had a cylinder 1 misfire that was fixed with a new fuel injector. otherwise no codes or cel for several 100 miles. Since i am new to the 2.4 compared to my 2.2 2006 model i wasn't sure at first if this was normal as i got to learn the car. A lot of roads around me are 35mph speed limit. What i've been noticing is that unless i accelerate to 38-40 mph, it will stay in 3rd gear / 2000 rpm... if i go a little faster, it will drop to 4th/1500rpm, and it will also stay in 4th if i slow down to 35mph again. The car runs/drives fine, but also gets really crappy gas mileage compared to my 06. like 18-22 verses 24-26 for exact same driving situation.
A quick SE/AI check mentioned fluid could be a little low or a faulty sensor or something else. I will be jacking the car up to check level of fluid later, but meanwhile was wondering what the experts suggest.

 

Good find, yes check the transmission fluid level, clean the MAF sensor and the throttle body. Use CRC MAF cleaner and CRC throttle body cleaner. Definitely do not use carb cleaner or brake parts cleaner!

 

If a sensor was bad there would be a CEL.
The shifting is a matter of demand/need not speed or RPM.
Are the rear brakes adjusted correctly; too tight will affect MPG.
Sounds like you might be driving a bit aggressively, the shift points seem about right. The 2 cars have different AlGoreithms for shifting.

 

Thanks for feedback guys. i figured it wouldn't likely be a sensor since no CEL. I haven't checked the rear brakes but it doesn't seem to slow down overly fast when coasting. I will check those too.
i did wonder about shift points being different. Just figure if running in 3rd a lot instead of 4th on the slow roads, that'll definitely affect mpg. And not since my last LT1 roadmaster have i been driving aggressive as a default.
I did test more spirited acceleration with the 07 and i can tell a difference in power over the 06 2.2. But since my 06 has long passed the 200K mark i've babied that one most all the time as i don't want to have to do a timing chain job in the near future. So my overall driving habits have mellowed substantially over the past several years. Got nothing to prove to others (other than the satisfaction of driving a car that's paid for and is good enough for my current needs)

So, to do list - check T fluid, clean MAF and TB with appropriate cleaners and check rear brakes...... Al Gore aint got no rhythm :-D

 

I don’t think your transmission even has the same final drive ratio as your 2.2 did. It’s meant to be a sportier ride.

 

Same 4T45E transmission but different transmission control module program. So yes it’s sporty shifting. Especially with the FE3 suspension.

 

Yes, a quick non-authoritative Google check says that all LS and LT automatics (and Pontiac G6 base) had 3.91:1. SS had 3.29:1 though.

Cobalt had 3.63:1. HHR that needs a used transmission might end up with one of those, as they’re easier to source.