Hi everyone. I had the 100k mile service done on my 2013 G37 sedan about 4 months ago - spark plugs, clean throttle bodies, fluid replacement, etc. I was getting 19.9mpg consistently for the past 5 years. After the 100k service its dropped down to 18.8. I took a 400 mile trip with mostly freeway miles and only got it up to 19.2mpg - usually get over 21mpg. Any idea what they could have messed up? No check engine light. But something is definitely wrong. Was hoping for some insight from the group before I took it back to the dealer. Thanks in advance.

 

If the dealer disconnected your battery during the throttle-body cleaning, that would have erased some learned parameters in the ECU. It'll take awhile for the ECU to generate those parameters again.

That said, you should have gotten better than 25 MPG on a 400 mile, mostly freeway trip. Maybe an O2 sensor is dying?

 

Thanks for the reply. Lets see what excuse the dealer comes up with tomorrow.

 

You check air pressure in tires and what was your mpg before summer blend gas

 

Took the car over this morning. Hit them up with the possibility of an O2 sensor failing - it would have thrown a code. Hit them up with maybe the tech damaged the Mass Airflow Sensor when cleaning the throttle bodies - it would have thrown a code. I asked what they were going to check, we are going to check for codes. Service Advisor only knows codes. If there are no codes, its not broke.