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I have a ford focus 2002. It has an idle problem. At a stop the idle will vary from normal down to about 500 RPM, almost stalling. It does this variation very cyclically, every 5 seconds or so. Recently while driving I hit a hard pothole, and the problem stopped (it has been gone for about a month now) so it seems like something was loose? I am waiting every day for the problem to return. Any ideas?

  • I think you should check the vacuum lines connections and see if there is anything lose – method Nov 7 '16 at 20:45
  • A MAF or MAP sensor that's gone bad is a common cause for rough idling as they call it, if that's what you mean. It can't properly measure the incoming air, and thus it can't properly decide how much fuel to inject, causing a poor combustion, and rough idling. – Bart Nov 8 '16 at 10:03
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    Idle air control valve, maybe? – Mysterfxit Jul 6 '17 at 23:47
  • I'd blame the crank, cam shaft sensors or the idle control valve – user38183 Nov 29 '18 at 7:10
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That is what it sounds like to me, the pothole shifting something.

things I would check

  • look for cracking around the rubber or plastic vacuum lines
  • is this an automatic or manual? if it is an automatic and it does that shift to neutral and see if it stops
  • was your air conditioning on before? or did it suddenly stop working after running over the pothole? It could be you had a loose wire turning the pump on even if the switch was off but this is unlikely. But this would be a consistent interval and if it was shorted it could bypass the computer which would increase RPM when it runs.
  • Do you have a large sound system? if so and you crank the bass this can put a lot of resistance on your alternator.
  • check the wires going to your fuel pumps many cars have 2 for fuel injection systems. The pothole could have made a connection work better or jostled a bad brush on the pump motor.

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