Rumble in gear at stop, but fine in Neutral.

Everything I've searched for has pointed me to the IAC valve and TPS. After digging into this car twice, I'm pretty sure it has neither (they're just built into the the throttle body?). I thought mine was 2006.5, the kiapartsnow site says “2006 Kia Optima Produced Before SEP.2006


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Would you characterize this as a misfire, or a mechanical rumble like something has come loose under the hood? Did you clean the throttle body butterfly valve to decarbon as much as you could clean the area? What if you come to a stop in gear but keep your foot on the gas a little and of course press the brake harder to force the stop, the idea here is to keep the throttle open a little to allow more air in, once stopped, release the gas pedal, WHAT HAPPENS?


I would not characterize it as a misfire nor something coming loose, just a very uncomfortably low idle (but only in gear, when in Neutral it goes back up with no rumble). If I could just adjust the idle speed I would try that but haven't found a method with this model. Pressing on the gas a little with my foot still on the brake does help get it out of the uncomfortable range.

I did clean the throttle body butterfly valve which was dirty, but not excessively, and cleaned the contacts inside the plastic part of the throttle body with contact cleaner. Neither seemed to change anything.


Without info in front of me I would test the volts to and from the TPS, for example, there may be a wire with 5 volts, a ground with less than .1 volt and a wire with around .5 volts. Can you post your readings please.

My 2 foot method of testing was to come to a stop without allowing it to get too low of an idle speed, maybe dont let it drop below 1000 RPM and then release after the full stop, I would want to know if it never rumbled like that? Do you have a hotwire air flow meter or digital on this vehicle, it also can be cleaned but use AFM cleaner, not carb cleaner.