Runs rough with a new brain

Tiny
VICTOR S HALEY
  • MEMBER
  • 1999 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 25,000 MILES
Brain went out in my vehicle had to replace it with a used brain having trouble getting it to idle right.
Saturday, May 4th, 2019 AT 6:46 PM

1 Reply

Tiny
CARADIODOC
  • MECHANIC
  • 33,871 POSTS
The most common symptom is the idle speed will be too low until the new computer relearns "minimum throttle". Until that occurs, you may need to hold the accelerator pedal down 1/4" for the engine to run. You won't get the nice idle flare-up to 1500 rpm at start-up, and it may tend to stall at stop signs.

To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.
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Saturday, May 4th, 2019 AT 8:27 PM

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