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I bought an 05 Kia Spectra EX for my daughter. The engine is throwing a P0507 code which is Idle Air RPM greater than expected. I did some research and apparently this is a pretty generic code that can be caused by a variety of issues. Is there a best order to step through the various things that could be causing? I fear it is a vacuum leak which I'm not keen on chasing because I am not that experienced (but I am willing to learn) and it sounds like it can get really tricky trying to diagnose that particular cause. I do have the Haynes manual and I am comfortable underneath the hood even if I am not that experienced. As far as the engine behavior goes it definitely seems to be erratic, sometimes it idles high (even when having been operated for a while) and sometimes it idles at what seems to be a more appropriate RPM.

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I would definitely start with cleaning things before attempting to replace them. A simple solution may be to just clean your throttle body and idle air control valve (iac). Look at the air filter for large blockages just as an extra precaution. Take an overall glance at each intake piece to make sure nothing is disconnected, cracked, or broken and go from there. Hopefully you can find something simple before replacing anything.

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  • Dalton said it exactly right. Go over each and every vacuum hose on the engine. Gently squeeze, and check for cracks, burn marks, etc... Other possibilities include brake vacuum booster, Exhaust Gas Recirc stuff, Idle Air control... but check hoses first!. Also consider purchasing a Service manual from Haynes or Chilton ($30 well spent.) That will show you exactly how to check each of the things that could be causing troubles.
    – zipzit
    Jun 17, 2016 at 20:36
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The fact that its intermittent does not rule out a vacuum leak but makes it less likely. A common cause is failure of the idle air control valve (IAC). It can be tested by applying 12 volts to the center terminal #2 and then applying a ground to the outer terminals. It should open when #1 is grounded and close when #3 is grounded.

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