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?
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.