the check engine light of my 97 civic HX came out today but its running fine, but the gas mileage is only 28 to 32 mpg, considering that its engine id VTEC-E (economical). when scanned, it was the no. 1 02 sensor running too lean..

what could be the cause of this?

what should be the first step to do?

what is the effect of this to my engine

 

Make sure you have the right 02 sensor. The HX primary 02 is a wideband type that is very expensive.

 

i aheva 98 hx, first off, just to keep in mind, if you but a sensor from ebay, you can get a OE NTK brand sensor for 155-170 which is waaaaaay better than paying 606 at the dealer or 400 at a parts store. anyhoo, this only applies if your car is manual tranny, is it? but anyways, if its a system too lean code, you have to find out if its becuase the sensor went bad or more usually so it means that the engine has reached its maximum enleanment, and so it set the code, so you can find out the cause, basically, the onyl things that can cause a lean code, is a restriction in the fuel supply, or pressure, or something letting secondary air in. such as a vacuum leak. the effect to your engine, is once the light is on, and while its on, its runs on a fixed map, and doesnt use the o2 for fuel trim, and now your mileage is poop

 

If its running lean tahat means your car iz putting more o2 then fuel..

 

thanks guys, appreciate your advice. i will check my fuel filter and the vaccum lines.

by the way, the hose that is going to the valve cover and the air intake is busted is busted, would it be the cause?

 

mine is manual tranny..

 

The symptoms point to needing a new oxygen sensor. You car is old enough that this is not surprising. Go with OEM only for a new oxygen sensor. Consider http://cgi.ebay.com/ebaymotors...89080

 

i already fixed it man, there is a vaccum leak. and i clean the MAP sensor..

 

yea if it was the hose on the pcv valve side, trhat was busted, yes that affects the o2 sensor, and it sis possible, but on different motors more likely that if the vent hose from the valve cover to the intake pipe, that can cause the code as well.