Please help anyone, Rpms jump and fall! -
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post #1 of 3 Old 03-13-2012, 10:57 AM Thread Starter
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1999 XJ Cherokee 
Join Date: Nov 2011
Location: Pembroke
Posts: 23
Please help anyone, Rpms jump and fall!

My CE liight has been on and i finally checked it out, and i plugged it in. 2 codes came up, but this is the only one i remember; P0171. System Too Lean (Bank 1). but before you look that up, i know i have a crack in my manifold, and i understand it needs to get replaced. but whenever my engine heats up to normal temp, ill keep my foot steady and my rpms will just drop, then shoot up, and go up and down over and over while i keep my foot steady. but if i go over 3k it wont do it. after i let the rpms go back down it will want to die so i have to either put my food down and feel my jeep jump and jump and jump or go 3k plus on the rpms and go flying by. It does become very difficult to drive this way. especially when their are people in front of you.

If you were on the road next to me or in the passenger seat, it would look like i would stomp on the pedal and right away let go and jump on it again and let go, it is very frustrating so if anyone could help i would appreciate it! i will find the other code later and post it in an hour or two as I am working

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post #2 of 3 Old 03-13-2012, 11:03 AM
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1989 XJ Cherokee 
Join Date: Apr 2006
Location: montana
Posts: 1,352
Give this a try and seed what happens to the code
A code P0171 may mean that one or more of the following has happened:
  • The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
  • There could be a vacuum leak downstream of the MAF sensor.

1989 XJ, 5spd, np231 with bjconversion SYE , re3.5, 33x12.5r15 BFgoodrich ATS, D30 F, Dana 44 from 87 with 4.56s, Custom front bumper.

94 yj: stock everything and 4 angry squarrels under the hood.
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post #3 of 3 Old 03-13-2012, 11:21 AM
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2000 XJ Cherokee 
Join Date: Apr 2002
Location: out in the garage - Minneapolis
Posts: 28,366
Without knowing all the trouble codes, there is little you can do. Download and post all the exact code numbers.

What you can and should do first, is fix the cracked manifold.

P0171 Causes:
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust manifold leaks
- Incorrect fuel pressure
- Lack of fuel
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

“When the people find that they can vote themselves money, that will herald the end of the Republic.”

- Benjamin Franklin
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gas , idle , issue , jeep , rpm

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