i have the model in .idb but I can not place a car in the XY plane as it is grey polygon and it does not show the geometry. attached the geometry .idb

I believe this is related to WinProp.

The attached idb file looks OK. When you import the car, please make sure the coordinates of the car are reasonable, especially, the z value should be bigger than 0. 

Normally, when importing a new geometry, a group number is given. Please use "group manager" to search for the imported geometry in the 3D display of WallMan.