QuestionBought the car used check engine light is on and it reads p0174 too lean bank 1 and 2, replaced mass air flow sensor and car worked perfect for about 1 week. Code p0174 came up again and now it jerks really bad a few times then it stops, I took it to the dealer and they said it was. The m.a.s. which I changed and it worked for about a week, but now this please advise thanks 4 your time.
AnswerP0174 indicates a lean condition on only bank #2. Anything that can cause a lean condition can cause this code. This doesn't necessarily mean bank #1 isn't running lean-- often, this code sets when both banks are lean but only bank #2 is lean enough to meet the criteria to set the code, and bank #1 is almost lean enough.
So, the first step in attempting to figure out what sort of problem is present is to use a scan tool look at the fuel trim values (amount of time the injectors are kept on in comparison to the expected necessary amount) and compare from bank to bank. You'll want to see the values in freeze frame data (snapshot of data at the time the trouble code set) as well as the values in current data (live data readings) when the engine is running while at operating temperature. This will help tell you whether the problem is something that will affect only on bank and whether it's something that's intermittent or currently present.
I'm going to group the potential problems in four categories below. Note that some problems can appear in a number of categories.
Problems affecting one bank only:
defective upstream oxygen sensor
intake manifold gasket leak
plenum gasket leak
Problems affecting both banks:
defective air flow sensor
large vacuum hose leak
low fuel pressure
excessive methanol (or other alcohol) in fuel
leak in bellows between air flow sensor and throttle body
Constant problems:
defective upstream oxygen sensor
intake manifold gasket leak
plenum leak
defective air flow sensor
large vacuum leak
excessive methanol (for one tank of fuel only)
leak in air bellows
Intermittent problems:
low fuel pressure
defective upstream oxygen sensor
defective air flow sensor
air bellows not securely attached causing intermittent leak
Without a scan tool and/or a fuel pressure gauge, the only thing you'd realistically be able to check for would be the air/vacuum leaks.
My best recommendation is to return to the dealer that did the original work/diagnosis and explain that this hasn't fixed the vehicle. A reputable place of business will give you due consideration because of an incorrect diagnosis.
