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Old 09-12-2019, 12:47 PM   #1
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Up & Down RPM when Idling - 05 Focus ZX5 Se Automatic

New to the forum here! Also, new owner to a 2005 Ford Focus ZX5 Se.

Currently having my idle RPMs without AC stays at about 500-750 RPM and jumps up to about 1000 RPM when stopped and on drive. This happens occasionally and when the car is warm. When the AC is turned on, the RPM dips to about 250-500 RPM and revs up to about 1000-1250 RPM.

Just got the car recently at 85k miles.

Previous owner replaced:
- Catalytic Converter
- Motor Mounts
- Timing Belt
- Spark Plugs

I replaced recently:
- IAC Valve

Problem still happening, any ideas?


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Old 09-12-2019, 06:22 PM   #2
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Look for the typical vacuum leak that occurs on that engine when the PCV hose buried behind and under the intake manifold begins to leak from age.
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Old 09-12-2019, 07:26 PM   #3
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Thank you for the info. I'll check that as soon as I got time. I also remembered the guy who sold me the car saying that the issue occurred when he changed the catalytic converter and that procedure had him remove the battery. Do you think an improper idle relearning process would mess with it?
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Old 09-12-2019, 08:38 PM   #4
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They will relearn idle automatically in the next half hour of running after battery is hooked back up. 15 minutes if you dedicate to it. Ford does not make that a thing you need to do by initiating it yourself, the software does it with no command to.

Meaning that if any incorrect idle is relearned, that faulty parts caused it that were not working correctly. Your hi/lo idle is likely due to it, the PCV hose can suck open to rev high, the IAC corrects back down low and then the leak revs high again, often the leak is opening up and closing off to do that, the IAC then chases it with no resolution since the condition does not stabilize. Most IACs get changed when there is nothing wrong with them, chasing rpm up and down actually shows one is trying to control the idle. It's just that the conditions are changing from second to second to prevent that.

Always listen to but never 100% swallow what the previous owner says, they are often very untruthful or wantonly unknowledgeable (take the engine, if that year is right there is NO timing belt, chain ONLY), if a car has such a simple problem then why are they getting rid of it commonly at a loss to them? You as the new owner have to accept the physical conditions of what the car presents rather than assume the other owner was right. Removing a battery would not do that unless there is something else wrong.
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Last edited by amc49; 09-12-2019 at 08:46 PM.
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Old 09-12-2019, 09:38 PM   #5
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Understood,

Thank you for the info, the main reason why I'm looking for alternatives right now is because:
1) Potential Cost: If a mechanic were to do the change for the PCV hose, how much would it cost me?
2) Conflicting info: Currently saw two sources where one says I had to remove the entire intake or I just have to jack up the front of the car and can reach and replace the PCV valve/hose from there. So if I were to do the repair myself I'd have to figure that out first (since I usually can only do the repairs on the weekends).

On that end, do you know by any chance where the PCV would be for this model?
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Old 09-12-2019, 11:21 PM   #6
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Old 09-20-2019, 11:54 AM   #7
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So I was able to replace the PCV Valve and the Hose, but the problem still occurs. Now though it only happens with the AC on, and very rarely with the AC off.

Any ideas? Gonna have the battery checked for any potential electrical issues.
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