Recently I bought a short ram intake hope the MPG would increase in my civic. After having a new head installed I saw my MPG go from 32/33MPH to 36/38 MPG. Already had the short ram and figured it would not hurt anything to install it after the new head. MPH went back to the low 30's Went back to stock but the MPG did not improve. (2 tanks since the switch back to stock) I have ordered a new air temperature sensor to see if I might have done something to the old (still installed because the new one is not here yet) one while switching back and forth. Was this a good move? Any other possibilities on the lack of MPG?

 

When was your last tune up (plugs, wires, cap, rotor, ignition timing)?

Any CEL codes?

 

The Engine light was on for some misfires in the 1 and 2 cylinders. I replaced the plugs and wires a few days before the new head was put in about a month ago. Full tuneup was about 2 years ago. Dim engine light since the new plugs and wires.

 

Well if you got a missfire on cylinders 1&2 your not gonna get better gas mileage. Put some injector cleaner with premium gas next fill up, I did had the same problem with my old 4 door eg, it worked for me. Just a thought, tho man start small.

 

You need to do another full tune up. Use OEM ignition components.

Dim CEL?

 

short ram intakes increase intake air temperature and if the ambient air temperature outside decreases, so will the fuel economy benefits. Frankly I think it's possible your car needs a tuneup with the first order of recommendation is replacing that PCV valve of yours along with checking to see if you have any vacuum leaks.