My 93 Prelude Si has an H23A1 motor and when I installed my aftermarket intake I took out the air intake silencer as well. Well I unhooked a small vacuum line from the silencer and plugged it since there was nowhere for it on the new intake. Well I finally traced the hose and it runs to a small plastic box close to the batttery with a two wire sensor. Then the hose runs out the other side of the box and back into the intake manifold. I was just wondering if anyone knows what the sensor is. I was thinking air intake temp. sensor but I thought they were actually on the intake manifold. If it is not an ait, then is it for emissions? I don't have it hooked up at all right now and my car doesn't seem to run any differently. Any help would be appreciated

 

this is just a guess but maybe its the MAP sensor? anyone else?

 

Evaporative Control Canister is my guess. Black cylindrical thing? with a drain hose out the bottom? If it were a MAP sensor, the car would most DEFINATELY run different, but if it's the Charcoal Canister, it's just emissions control stuff, it won't make a drastic difference, but could cause you to fail visual emissions checks if it's not hooked up.