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???

 

Possibly a vacuum leak.

 

wouldn't a vacuum leak cause him to run lean?

 

You'd think so with the extra air getting in. What actually ends up happening when there's a leak is the computer sees that the throttle is closed via the TPS and that the IM vacuum is low (or the pressure is high) via the MAP sensor. It is programmed to know that pressure changes with altitude and so decides that the low vacuum means the vehicle is at a very low altitude, where air pressure is higher and the air is denser. Because the ECU believes that the air entering the motor is denser than normal, it supplies more fuel to compensate, creating a rich condition.

 

wow nice to know i always thought that

vacuum lines = lean
o2 sensor = rich

 

check the throttle cable and the linkages. it should move freely.