Fuel Trim malfunction check engine light

Alright guys my CEL light has been on ever since i have bought the car and i have gotten the code checked and this is what is says. P0170(Fuel Trim Malfunction). There are 3 possibilities on what it can be from what i have been told: 1.O2 sensor, 2. Ignition misfire or vacuum leak, 3. Fuel Injector. These are the symtoms of the car: 1. In the morning when i start up the car, it stumples like it wants to cut off for about 45 seconds, like it idles at around 150rpm's for about 45 seconds. But it idles better after that. It idles around 14 vacuum, which i think is kind of high. But i know it can't be a ignition misfire because it did it when i bought the car, and i swapt out and put in new NGK wires, and NGK 6es plugs and properly gapped them., and it still runs like this. So, this leads me to believe it is a vacuum leak, fuel injector, or 02 sensor. But sense i am installing a downpipe this sat,i dont have to worry about the one after the cat(since i wont have one, so i am gonna get the one before the cat. How can i check for vacuum leaks? Anybody have any ideas on which one of those three it might be? Any help at all would be appreciated.


This saturday i am gonna check for vacuum leaks.

any ideas?

I don't know about the vacuum leak thing, but I know when my car tripped the CEL for a fuel trim malfunction, it was my front o2 sensor. I bought a new one and my CEL was gone :) Good luck

i changed my o2 sensor and it didn't work i still have it

I have the same problem, but from what I have read its most likely the front o2 sensor like what guitarXgeek said. Do you get bad ass milage? I plan on changing mine when I get back!

Did you get the codes cleared after changing the O2 sensor? They usually wont go away by themselves (a few of them will). If you cleared it and they came back, I would look into airmetering next. I would log airflow at idle and see what it is.

Did you get the codes cleared after changing the O2 sensor? They usually wont go away by themselves (a few of them will). If you cleared it and they came back, I would look into airmetering next. I would log airflow at idle and see what it is.


yeah i clear out the code with my actron 9145 scanner but after 2 days it came back on and man I sure do get a bad gas mileage but yea im going to check my air metring next......peace!

vac should be between 17 - 21 during idle. you could have a leak somewhere and/or a bad O2 sensor. go over all vac lines, especially the EGR valve lines. if the EGR valve is not working properly it could affect gas mileage.

I fixed mine by removing the bulb, lol :grinyes:

I fixed mine by removing the bulb, lol :grinyes:

Way to fix the problem. Great advice too, this guy wants to actually make his car run correctly. :nutkick:

I fixed mine by removing the bulb, lol :grinyes:
what a moron :loser:

wow, aparently no one has a sense of humor on here.