donbrew

The computer gets no signal if the ignition is turned OFF and especially if the wires are disconnected. See the big red NOTE. That is the reason for step #5.

Why would you crack the plastic case to clean the gears?

In all my years of abusing engines, I have never managed to get gunk built up enough to interfere with the butterfly. I have seen it happen. My dad's '67 Chrysler once had the choke stuck.

Silverfox

+ Common Sense tells me that the Air Filter cleanliness is another critical part of keeping the system functioning properly. Much more so then older technology auto's.

In those days I used to concentrate more on the Fuel and Oil filter then the Air filter.

Then when I thought about it, I could pop it out in 15-20 seconds ... See how it looked, Bang it on the bumper a couple times and put it back in. I did usually put a new one in at about 40-50,000 mi.
Fortunately I have never lived in a dusty environment.

Don: I too am still thinking about the Tranny as a possible, so once I get time to do the throttle body/Maf sensor, that should reveal the next step if necessary.

Just finished the front stabilizer bushings (Stock GM) with some silicon grease on them and the 2 Moog stabilizer end links.

The Bucket List is getting smaller.

I wish I still had my heated garage from years ago.

Silverfox

Casa Del Gatos

I notice the one for the 2.0 also doesn't mention the "relearn" process. Does that mean it is not an issue and I can scrub mine with a toothbrush and the CRC spray?

That's what I did with my Mustang and it made a huge difference in smoothness of accelerator.

prod

Actually what I think is more of a factor is the vented oil and carbon crap that is pumped in after the air filter.

Oldblue

This will help with that

https://www.chevyhhr.net/forums/2-2l...ormance-58332/

boltfan1953

We have a 2.4l 07 HHR and kept getting P0121 code. We replace the Throttle body and pedal. Throttle is stuck on 25% and wont go down. Any suggestions?

Oldblue

I answered you in your other post, I moved that to its own thread, and not attached to a dead thread from 2007

whopper

and lets close this before it causes confusion over the multiple posts.