check engine light. code P0171

[TDWPgtp]

light came on, engines been starting and running rough...had it scanned, had the code run and now i have a list of a million different things it could be. does anyone know of any very common problems that may cause this code or anything to fix or check. the guy at the shop said this may be a very expensive and important problem so any help would be great

[richtazz]

P0171-System too Lean

This code can be caused by many different issues. First up, what year and engine?

[TDWPgtp]

ya i believe its on bank two. anyway its a 97 grand prix gtp. supercharged engine.

[BNaylor]

We only reference Bank 1 since we do not have a Bank 2.

As mentioned DTC P0171 indicates the system is in a lean trim mode. Ideal fuel trim = zero. Greater than zero indicates the PCM is adding fuel to compensate for the lean condition. If fuel trim is less than zero the PCM is reducing the amount of fuel to compensate for a rich condition.

There are many possible causes for this specific DTC and it may not be easy to pinpoint the exact cause if it is not obvious and further diagnostics or parts swapping is needed. With a full function odb-ii scan tool you can check short and long term fuel trim values and that may help pinpoint the cause better.

Here are some causes.

Vacuum leak . Check all vacuum hoses at intake system. Possible supercharger or LIM gaskets.
PCV Valve
Possible throttle body blockage (clean input screen and body)
IAC (idle air controller valve)
Fuel injectors (bad lower o-ring seal)
MAF sensor
EGR valve
Bank 1, Sensor 1 02 sensor (Pre-CAT converter)

[TDWPgtp]

ya thats some of the things i was told it might be. i checked the air intaked and throttle body screen and most of the hoses but havent got to the rest of them seeing as i only had about an hour. i was just wondering if there was a single common problem that happend on grandprixs to cause it for example like a certain specific hose tends to leak or something. thanks tho ill be sure to check all of those things

[BNaylor]

Nope. Just one of those diagnostic trouble codes you wish you'd never get but not specific to just Grand Prixs nor is there a single common fix. All I can say is process of elimination and cross your fingers. If you could get the short and long term fuel trim values we can tell you what direction to head or narrow the possibilities down.

[TDWPgtp]

for about six months i had been using 87 octane gas right after i got the car, cuz no one ever told me i should run premium. do u think that might have caused damage that lead to the code

[BNaylor]

Hard to tell if running the wrong grade gasoline is the cause since you can get this particular DTC even running the proper gasoline. So we would be speculating. But I am assuming you are now running premium unleaded 91 octane or better?

Try the simple causes listed first. Start with the MAF sensor. Disconnect it and see what it does or if driveability improves or returns.

[TDWPgtp]

i disconnected the MAF and when i did the car wanted to stall out. the overall feel was much worse than before. as it is when its connected it hesitates and doesnt really go anywhere till about 2000 rpm. there is also a very noticeable loss of power. im going to clean the maf anyway. is there any sort of gasket or sealent on it that i should be aware of

[Cursed 99 GTP]

Spray some carb spray at the base of the intake or by the vacuum lines. If the idle smooths out then you found your leak. I am dealing with the same problem.

[TDWPgtp]

i dont have any carb spray or parts cleaner. is there any household spray i could use? wd40 or anything?

[richtazz]

WD-40 or similar spray lubricants will work to find vacuum leaks too, but don't spray it anywhere near the MAF sensor, as the oil in it could mess the MAF up. If no vacuum leaks are found, I would strongly suggest getting it scanned and then post the short and long fuel trim values as bnaylor suggested. That may help point you in the right direction, rather than hit and miss guessing.

[TDWPgtp]

short term fuel trim is at 20. long term is at 16. i believe thats maximum for both but im not sure

[BNaylor]

For short or long term values you should indicate whether it is positive or negative. But since the DTC is P0171 we are assuming it is positive and above 0%. 20% is the maximum reading but ST and LT values towards 0% is what you should see. Basically you have an excessively lean condition meaning the PCM is having to add fuel to make it richer and keep the air/fuel mixture ratio at the ideal 14.7:1.

[TDWPgtp]

ya thats what the guy who scanned it said, we just have no idea what the cause is. we cant find any leaky vac hoses, im assuming the MAF is ok because the car doesnt try to stall anymore, and drivability was worse with it unplugged, there are no obstructions in the air intake or throttle body. where should i go from here