[TSM_Pikachu]

Yo man, that seems really weird. Did you reset your ECU?
If not, that could be a cause, also......when a CAI is installed people tend to step on the gas a bit harder to "hear" the intake and the engine. Im not saying you are doing this but it is a common occurance.
Also, you might not want to up your octane rating unless your car specifically needs something like premium. Im running 87 octane and getting about 25-30mpg now with my CAI on a 91 Accord.
I hope some of my babbling can help..........also there are other variables that could affect your MPG ratings such as fuel filter, plugs and wires, etc........

 

[TSM_Pikachu]

The filter COULD get dirty quicker but it depends really on where you live and what the conditions are around you.
Some of the guys here on SHO clean the filter at the end of summer and at the beginning of say......spring
Then again it really all depends on many factors.
Try this man, disconnect your battery for 15 minutes.........then reconnect it. start your car and let it idle for 5 min DO NOT touch the gas. Then turn the car off. Wait about 5 min or so, turn the car back on, reset the clock and see if that helps your mileage any.
To clean teh filter, i recommend buying a filter charger kit or something like that. 4 months of use huh? okay well unless you are always driving through dust clouds I dont think it would be immensly dirty. hahahaha
Also check to make sure you have done all your recommended service checkups and maintainence, these small things and some of the larger ones can really make a difference in the way your car performs.

 

[TSM_Pikachu]

pboilee: Uh, NO that is not why he gets bad mileage. hahahahha
If that was the case, when I stuck my intake on.....i would have gotten seriously crappy MPG.

Bonestock has a good point because i used to do that too. hahahah

Jocktheglide: Take a look at your filter, go get a recharger kit if needed. Then also reset your ecu as i said, those should yield you some gains.