Hello All,

I have a 2008 Honda Civic Hybrid 1.3L Engine with around 153,000 miles. Luckily I was able to replace the IMA battery when I purchased the car (30,000 miles ago) and was replaced by the dealership at no cost to me since it was under warranty. Besides that, the car has only needed minor repairs and maintenance here and there for brakes and oil changes and things of that sort.

About a month ago I had to replace the AC compressor and clutch because the AC system stopped working and it cost me a whopping $2300 to replace. Everything was working smoothly up until this week when I realized that I started to have a much lower gas mileage than I usually get. Even when I would have the AC on and working at full blast before with my regular driving habits I would average between 39-42 MPG. Currently, however, I am only able to get between 28-30 mpg and have been noticing some other issues with the acceleration of the vehicle and issues with the RPM gauge.

Currently, when I need to accelerate I have noticed much lower gas mileage than usual and the RPM on the car would spike up to over 3,000 even when I was only accelerating up to 30 mph. After going to my local mechanic and having him test drive it we thought the transmission fluid might be an issue so I went to the dealership to get that replaced this week, but the issue is still there. While driving on the highway I have also noticed that I need much more gas to maintain the coasting speed. This is causing me to use more fuel and hurts the overall fuel economy of the vehicle.

There are no lights on the car and the IMA battery is still charging and working as expected. I wonder if the issue might be stemming from bad spark plugs, bad oxygen or fuel sensor, or if the AC replacement is causing these issues. Any help on this matter would be greatly appreciated.

Best,
Mijungry

 

I'd start with the basics - fuel, spark, and air. I was facing a similar issue because I had a rip in the big hose that comes off the air filter box. Look around for any tears there. It's about the right mileage to need spark plugs, so don't be afraid to replace them! I'd go with dealership ones & spend the extra amount, the engine is finicky and there's no need to introduce more variables. Fuel supply obviously isn't an issue, so we can gloss over that for now.
Aside from using more fuel, have you noticed any other odd issues? The IMA battery charging weirdly, the a/c feeling more or less cool than usual, the auto stop not functioning correctly?
There's also a thing called the egr valve, and those can build up carbon deposits that make your car unhappy. Taking a look at that might help this link should help you figure out how to do that.
editing to add - a lot of "codes" for your engine and IMA will not activate lights on your dash. in order to access the sneaky codes, you can use a code scanner or stick a paperclip into pins #9 and #15 of your obd2 port. when your turn your car on (but not started), your dash will display some of those codes via blinking/flashing the IMA light & the odometer display screen.