How is it possible to visit Iran with our own car?
First off, if you are from US, UK and Canada, you are not allowed to enter Iran in your vehicle anymore. It was allowed if these countries passport holders were accompanied by a tour guide but the rules changed and there is no way to cross Iran overland. The only way is to transit the vehicle on tow to the next border.
* Not applicable to other nationalities, of course.
* Iran visa: recommended to apply through travel agencies for prompt response.
* Carnet de passage: No, Iran embassy cannot help. You should either apply through a company in your country or get one at the border before arriving to the border. The only possible borders are Armenian, Turkish and Azerbaijan borders.