what would make my Tiburan idle speed fluctuate from 800 rpms to 4000 rpms.

2003 HYUNDAI TUCSON
118,000 MILES
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EX3200
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I installed a used 5 speed transmission in my tiburon and when i first started it the idle problem was there, it was fine when i started the trans. replacement, I had replaced the tach/speedometer gear and sensor in the replacement tran. with the one from my old tran. Also I had the ignition switch on when I hooked up the battery post. would a surge from hooking up the battery mess up a sensor that controls idle? Any help would be greatly appreciated.
Jul 8, 2012 at 1:18 AM
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DRCRANKNWRENCH
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It probably would not affect the Idle Air Control Valve which is a servo that controls idle. It would more likely mess up the ECU if you had the harness hooked up, but then you would more than likely have other issues. I would check for vacuum leaks especially around EGR at exhaust.
To help here is a walk through diagnostic for your situation. I think pulling the trouble codes will be important. Any Advance Auto or Auto Zone will do this for free. You do not have to have a check engine light to have a trouble code present which would really help eliminate a lot of possibilities.
Just use the link below;

https://www.2carpros.com/articles/engine-idles-too-high

Try this one to;

https://www.2carpros.com/articles/engine-surges
Jul 8, 2012 at 1:35 AM