Ok, I put in an Airaid cold air intake, now the DIC mpg is very touchy, it goes up and down so much more than when I had the factory air unit. Is this common, due to the air flow sensor? I did manage to get the city/highway up to 29.3 today, about the same as before putting in the cold air intake. My HHR has 1700 miles on it.

 

I found that with my intake, the car is much more sensitive to my driving styles. This reflects quickly when I watch the DIC. It's really been a blessing and a curse. I love the additional power, but I am getting worse mpg's overall.

 

I baby my HHR. I drive 55 on the highway and don't gun it. Right after I installed it, my 14 yr. old and I hit the road out of the driveway, I gunned it and the DIC read 16 mpg, so I don't do that unless need too. Before I installed the intake, I babied it the same way.

Would synthetic oil increase mpg?

 

I lighter oil weight may increase the mpg and HP since there is less viscosity. Synthetic engine oil will just last longer than regular oil. There are some synthetics that claim more hp and mpg. Royal Purple is one of them.

 

I had a 93 Corvette a few years ago that I replaced the air filter element with a K&N and changed the oil to Amsoil .,and improved the gas mileage by 3mpg. Was hoping I could get similar results with the HHR.

 

The Royal Purple hp claim, though, was made after changing not just the engine oil over to Royal Purple but also the transmission fluid and rear differential, too.

Here's my plan on the HHR, which is currently @ 700 miles on the odometer:

1000 miles: change oil to Mobil Clean 5000 (conventional oil)

5000 miles: change oil to Mobil Clean 7500 (conventional and synthetic blend)

8000 miles: change oil to Mobil 1 (full group IV synthetic)

Thereafter I will follow the Oil Life Monitor for changing out the Mobil 1.

I am not a fan of the oiled cotton gauze after market air filters. If you ever do clean them you'll probably over oil them after cleaning and the oil will micro mist into the intake air charge during operation and slowly coat the Mass Air Flow sensor wires/diodes with oil residue which reduces their sensitivity.