My 05 TSX 6-speed with 90k miles gets horrible gas mileage. All fluids recently changed, new air filter, tires at proper psi, etc. I drive this car very conservatively and it rarely sees above 3500-4000 rpms. I get about 17-20 mpg with mixed 60% highway, 40% city driving. This is seriously unacceptable. My 06 S2000 gets worlds better mpg and I drive that thing way more aggressively all of the time.

Any advice what to check next? This is becoming extremely frustrating.

 

Any stored trouble codes?

 

What plugs are you using? Get good spark plugs, (yes, pay the money for the good stuff). Change them out. I'm at 189,000 miles, 24-27mpg, average, but that depends upon traffic patterns.

 

No check engine lights or codes at all. The car is 100% mechanically sound (aside from gas mileage, of course).

 

The previous owner provided proof that all prior maintenance was done at the Honda/Acura dealership. The car most likely has the OEM spark plugs in it. I'll change the spark plugs this weekend and see if that helps at all. Any advice for what spark plugs to use for best gas mileage? What are you using on your TSX?

Can the spark plugs solely be the culprit for bad gas mileage (about an 8 MPG loss over what the car is rated for), even though I am getting no other adverse effects from the current plugs?

 

See, I don't go by what the owner said when it comes to something as simple as plugs. I check for myself, and I change about every 2 years with the Iridiums. And yes, spark plugs alone can be a major factor in your bad gas mileage. The other is the actual tyre wear and age on the tyres themselves. In addition, driving habits (tail-gating , aggressive lane changes, etc)

The Spark Plugs I use are NGK/Denso - BKR6EIX-11 (Stock #3764).

We get about 370-390 mile range according to my logs. (about 26.4mi/gal - 27.8mi/gal)

 

Wow , I wish I got 370 , I get about 270 total , something is definetly wrong with my tsx, I'll do a plug and tire change and update. everything seems to be working fine though .

 

The most interesting part is that I'm now selling the car now that we have our 2017 Civic SI

 

I would consider doing a fuel filter change and then an ultrasonic cleaning on your injectors. I had www.precisionautoinjectors.com do a few sets of injectors for me and for 15 or 20 bucks an injector, they do great work. All flowing within 1% of each other and perfect spray patterns.

Another thing, is your car warming up correctly? Bad gas mileage can be caused by a thermostat stuck open as well.

How is it performing? Is it still running smooth and does it still feel like it has full power?