I would start by inspecting the spark plugs. DO NOT ATTEMPT TO CHECK OR CHANGE THE GAP!!!!!!!! They come gapped from the box and can be damaged very easily.

Be sure they are AC/Delco Iridium. Maybe just go ahead and replace them.

I reset the DIC at each fill up.

 

Clean the MAF sensor with MAF sensor cleaner, do not touch the filament, just spray the cleaner on it sparingly.
Clean the throttle body plate with throttle body cleaner, disconnect the negative on the battery first , then unplug the throttle body harness and remove the four bolts and gently lift the throttle body up to spray the intake side, gently wipe the butterfly plate , do not move it with your fingers as this can strip the drive gears which are only plastic.
Change the plugs as Don stated, be careful to loosen the plug a quarter turn then tighten an eighth turn to loosen any carbon build up and not damage the threads in the cylinder head.
Put the negative cable back on and tighten!
Fire it up and drive it.

 

So, I got the mpg up to 25 again, still not the 27 it used to be, but now my fiance is driving it and she complained about it not accelerating past 60 or 65mph, she says she floored it and it wouldn't go any faster.

 

I kept track of gas mileage for my HHR. This was the mpg distribution for my car while I owned it. While I lived in Florida, I did take it up to the snow belt a few times. Mileage will vary due to your right foot, AC on or off and outside temperatures.

 

I wish mine got that kind of mileage. As of Saturday it was at 25mpg with a.c. off tires at 36psi and mostly highway driving...meaning approximately 5 minutes city twice a day.

 

In post 13 you state you got the mileage back up to 25 mpg again, and a limited amount of speed, please list what you did to your HHR so we can help you.
Are your spark plugs AC Delco 41-103's ?
Is your air filter paper and new or cleaned, or do you have an oiled K&N filter?
Did any codes pop up?
Did you clean the throttle body and MAF sensor?

 

I raised air pressure to 36 from 35, and stopped using the a.c. for the first time since we bought the car.

Air filter is new acdelco, plugs are original acdelco, no MIL, I have not cleaned throttle body or MAF yet. As for the acceleration issue I was not able to reproduce it so I believe she may have let off during a downshift causing it to wind up but not launch. Its hard to diagnose any problem she has because she can't tell me what she hears as her imlant only works so well.

 

Standard trans, or she thinks shifting the auto trans is a good thing.

 

Its an auto and she does not mess with it, it stays in drive, I occasionally put in "I" but very seldom.

 

Then I don't understand post #17.