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P0171 and P0174 Service Engine Soon

This is a discussion on P0171 and P0174 Service Engine Soon within the Computer & Tuning forums, part of the LSx Technical Help Section category; I have a 99 firebird formula that i purchased three months ago and it had a New Hapshire title. Three ...

  1. #1
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    1999 firebird Formula

    P0171 and P0174 Service Engine Soon

    I have a 99 firebird formula that i purchased three months ago and it had a New Hapshire title. Three weeks in the ac compressor was replace due to spun bearings. About a week ago the "serivce engine soon light" came on and i had the codes checked and they came back as P0171 and P0174 which is "lean right bank" and "lean left bank". The first thing that i checked was the airfilter which was really dirty and it looked as if it had never been replaced by the perious owner. Looking further into the intake on the MAF screen was pieces from the seal from where the stock lid connects to the larger rectangular air resivor. There was also a hole in the tubing. I removed the MAF (cleaned it) and replaced the stock lid with a SLP and the air filter with a k&n. I though that this would most definitely fix the problem but the serivce engine light still comes on for around 3 days and then will go off for two. It will keep doing this on and off but will never stay completely off for long. Every once in while there is a winning/whistling noise that is pretty loud and can be heard from inside the car. Once the car begins moving over around 5 miles an hour it goes away. Can this might be related to the ac compressor or is that normal. I was look ing at other forums about these lean codes and some suggested that it was a vaccum leak. Can this be the case or is it something different? I also am unsure which lines to check for a leak. Thanks in advance for the help.

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    Veteran 0rion's Avatar
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    yeah, could be a vacuum leak. Check all the hoses going into the intake. Pay close attention to the pcv hose on the passenger side. Those like to crack where it makes a bend to go into the intake and it's on the inside part of the hose so you can't see it without pulling it off. After you verify there are no vacuum leaks ( probably is one though) you can look at your fuel filter and check your fuel pressure and things like that.
    The whistiling you're describing sounds like the a.i.r. pump which is normal.

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    1999 firebird Formula

    Where exactly is the PCV valve located? I have been looking on line to try and find a picture but was unable to do so. I also forgot to mention that it idles alittle rough some times and the tach reads a 1,000 rpm at idle until i out it in gear. Then it drops to around 500.

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    the pcv hose is one of the hoses that goes into the intake just behind the throttle body on the passenger side. I forget exactly which one it is but check them all. Pull them off and bend them around and look for cracks. Also, check for any air that could be getting in there after the MAF......that's what your issue sounds like to me. There's air getting in somewhere via a vacuum leak or air after the maf.

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    I just checked and there actually is a decent size hole in the front of the elbow that is connected to the throttle body and the PCV valve. Could this be the problem? What is that rubber hose called and how can I got about getting a part number so i can pick one up. Heres a link to some pictures on what part has the hole. The third a fourth picture showthe elbow to the right of the disconnected PCV valve. http://www.installuniversity.com/ins...sity/index.htm
    Thanks again for all your help!

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    Turns out the PCV rubber connector from the PCV to the throttle body has a tare in the front side. Contacted GM said it was part number: 12590632 for $111.31. Even on Gm parts direct it is 87.00 for a rubber hose. Looking at a previous post some one used a 5/16 fuel line for a 1.50 and ran fine. Is this okay to do?

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    yeah, that'll work fine. There's a pcv write up in the stickies in the general help section that has a ton of info in it.

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    Is this the correct thread that you were refeering to? Seems alittle more complicated then I would have throught. any more detailed directions?
    PCV Valve Recommendation / Housing Modification

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