2000 em1 p0172 code??
 

Hey guys have a 2000 civic si that just popped up a p0172 code. Recent work done on the car is new clutch, new o2, new knock sensor and new axles. Mods that are on the car, walbro 255, aem cold air straight piped with fouler plug mod (never had issues). Stock ecu. What do you guys think could have caused this code to come on?