i have a 92 prelude and i put in a h23 and it ran great. Then i deployed for 10 months and when i got back the gas milage went down a lot. averageing 240miles per tank (13.5 gal). I changed all the fluids and everything seems to be fine. no check engine lite, it just idles at like 2k in neutral. Anyone have any idea of what the problem could be???

 

check the tires pressure?

 

Tire pressure and alingment are good

 

If I were to bet, I would place a bet on the O2 Sensor.

 

I say read both MPG threads in the FAQ.