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98 LS400 extremely low idle


grandpa_spec98
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Idles fine when cold, I believe it is around 1,100 RPM, once it warms up, it idles between 200-400 in drive, if it is a little over temp it’ll idle at 200 in park and die in drive. No major vac leaks and no CEL. Injectors recently replaced but the issue existed beforehand. Also noticed what I assume to be the throttle body motor making a loud humming with the ignition on and the car off.

(UPDATE)

Car shows a CEL and “CHECK VSC” appears

  in the dot matrix screen, idles up to 800 sometimes, other times it does not. Have not checked for codes.

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Edited by grandpa_spec98
Unwanted files, could not delete.
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So the throttle body wasn’t all that dirty, got a small cleaning and the motor was still acting up. Upon cleaning I noticed a connector where the throttle cable connects to the throttle body. (Shown Below)9A5A89BC-BDF7-4765-B9EE-4FBED656C4DE.thumb.jpeg.ec25ed2637b23f355e49b31c033d3897.jpeg

This connector was loose upon inspection and it turns out the clip is broken off. I would assume this is the throttle position sensor. Out of curiosity I started the engine with this connector unplugged and some strange but expected behavior followed. The idle was where it should be, on the dot if not a little high. As expected, there was no throttle response unless the pedal was mashed to the floor. (Shown below)

 

So my question is, could the throttle position sensor have to do with my low idle, or did it trigger a failsafe somewhere in the ECM that told it to just keep running, no matter what.

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