^ Smoothing groups for sure. if I were you i'd select the whole body of the car and clear all smoothing groups, then go back through and assign them accordingly.
Add an Editable Poly modifier if you haven't already, select the Polygon subselect mode, and look for Polygon Properties (I think). It's a grid of 32 little buttons, underneath or above it should be a button that clears your smoothing groups. You can then select individual polygons and assign smoothing groups to control the normals of the model.
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