1999 Jeep Grand Cherokee Laredo running rough?

My Jeep Grand Cherokee Laredo 4.0 has been running fine until the CEL came on. Pulled the code and said P0171 (system too lean bank 1). Then the cel light turned off but came back couple days later. I noticed the idle is very low ( 6rpm and almost stalls) and it usually idles at 7-7.5 rpm. In park it’s slight feels about like it’s about to die out but in drive the vehicle drops to 6k rpm(sometimes to 5k rpm) and the vehicle shakes like crazy and feels like it’s about to stall. I also smell a aroma of gas(running lean) but I couldn’t find any leaks anywhere. It does have 170k miles on it but I maintained it very well. I did clean the throttle body but that didn’t help. Is there any test that I can do to check if it’s the fuel pump, iac, tps or 02 sensor. I don’t just want to be Replacing everything and not finding what was the problem? Anyone had this problem before?

6 Answers

  • Jason
    Lv 7
    1 month ago

    Check for a vacuum leak. It's usually one of the little elbows on the intake manifold. 

  • not
    Lv 7
    1 month ago

    Lean code with rough idle is likely a vacuum leak. You'd maybe hear a hissing noise from the leak if you pop the hood and listen to it run. You have some plastic and rubber hoses attached to the intake manifold, good chance they are deteriorated. Even detached because they are deteriorating. Visual inspection is helpful if you know what you are looking at. You can test fuel pressure and rule that out. You can follow the instructions in repair manual to diagnose the code. A smoke machine is a safe way to check for vacuum leaks. It's thousands of dollars of tools or throw parts at it. If you can't spot something with the vacuum hoses then just take it to a professional and pay for a diagnosis.

  • 1 month ago

    Vacuum leak/ FI/ O2. Start easy/cheap and go from there.

  • Anonymous
    1 month ago

    1) A strong possibility is a bad fuel injector seal in bank one. That would also explain the fuel aroma...vaporized fuel under pressure getting past the seal.

    2) Get a clue. It's not idling at 5k lor 6k rpm. The indication of 0.6 rpm on the gauge = 600 rpm. 0.7 to 0.75 = 700 to 750 rpm.

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  • 1 month ago

    You need to do some testing to determine the cause of that code. Smoke test the intake manifold to see if you have a vacuum leak. Then you need a mechanics scan tool to check all the engine data to see if any of the sensors are out of spec.

    Source(s): Mitsubishi Master Tech
  • Rick
    Lv 6
    1 month ago

    check the 02 sensors in the exhaust ..............................

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