Rough idle stall

2000 JEEP GRAND CHEROKEE
180,000 MILES • 4.7L • V8 • 2WD • AUTOMATIC
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TERRI FOSTER
  • MEMBER
  • 1 POST
The vehicle was having trouble cold starting, it finally turned over after third or fourth try. Then one day it stalled in traffic and when I got it into a parking lot I tried starting it and the whole engine shakes really bad and won't stay started. I have codes for multiple misfired and also lean fuel. I checked codes when it broke down and it said MAP sensor. so i replaced that and still engine shakes bad and won't stay started.
May 18, 2019 at 3:53 AM
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KASEKENNY
  • ✓Experienced Mechanic
  • 18,907 POSTS
Hi Terri,

This sounds very much like you have a vacuum leak. What happens when air comes into the engine past the MAP sensor is the PCM doesn't know how much air came in because this is called unmetered air. So it adds enough fuel for the amount of air that it does know is coming in but this is not enough fuel. So it runs lean and misfires and sets the codes that you have. Plus it will run real rough and even stall out. Exactly what you are experiencing.

Here is a guide that will help explain this a little more and how to find where the leak is:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

https://www.2carpros.com/articles/engine-vibration-at-idle

Please let me know what you find and we can go from there. Thanks
May 18, 2019 at 5:27 AM
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