Rpm drop

Discussion in '2011+ Mustang GT 5.0L Tech' started by 1badote, May 5, 2019.

  1. 1badote

    1badote Junior Member

    Hello and thanks for any help, I have a 2011 mustang 5.0 and it only has 38,000 miles completely stocks expect axleback mufflers and I noticed while I’m sitting at a red light and the air is on when the Radiator fan kicks on it drops between 300 and 500 rpms then it’s smooths right back out it only does it when the fan kicks on, my wife works at advanced auto and we put a brand new battery on and tested the Alternator and it’s good. It’s not reading any codes I took it to the ford Dealership and they said everything is normal..... so my question is that correct is it normal and if not what could it be?
  2. Shocker10101

    Shocker10101 Junior Member

    Mine was doing this too and it ended up being a bad o2 sensor. Do an idle relearn procedure once you replace the o2 sensors and hopefully that is the issue. Hard to know for sure without actually reading what the o2 sensors are saying, but this was my issue.
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