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does larger throttle body affect idle when cold?

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we have a commod mod where i live, which is to fit a larger throttle body to the factory intake manifold. mostly done with 1fz and the fitted throttle body is half an inch larger. its is from nissan infinty.

i noticed every time this mod is done the engines stall and keep turning off when cold. its not even that cold (like 20 C). common solve is either opening the throttle a little bit more until the engine is relativly hot. then it runs smoothly, or increasing the throttle oppening form by ajusting the screw, which rises the rpm permenantly which is somewhat annoying.

my questions are: can i fix this only with tuning. without adjusting the throttly body opening?

the real question is i really want to know why is this happening. its not that cold, but when it is hotter it runs better.


Is the ecu tps input being recalibrated? Are these DBW or conventional with idle bypass valve?

it runs toyota 1fz factory ecu. cant be adjusted. no calibrations done. they use cables and i think they have bypass valve since they are factory nissan throttle bodies.

the thing that confuses me is why does it get better when it is hotter? i mean if its some calibration to be done or mechanical issue wouldnt it keep stalling even if its hotter?

Sounds like there isn't an effective bypass setup and the factory tune doesn't make enough torque with that airflow. Oil viscosity chanhe with temperature could be enough to hold it back. I wouldn't think it was likely but the different thermal expansion rates of the blade and bore might mean there is just a bit more air getting through when the throttle body heat soaks too.