So why does the author insist on sanctioning the automobile industry? The Washington Post article states that Iran has been "scouring the world for carbon fiber". High quality carbon fiber is evidently a key part of advanced stage centrifuges and so, there apparently are already sanctions on Iranian purchases of high quality carbon fiber. According to ISIS (Institute for Science and International Security), as a result of this, Iran has begun to produce its own carbon fiber (albeit of low quality).
I may be wrong, but from what I understand of the evidence, the target of the sanctions is not the actual industry itself, but those who run it (IRGC), who are also known to have attempted to proliferate materials important for nuclear activities. Therefore the argument should not be that the industry, the cars or the materials themselves that are a problem, but rather that those who lead the industry are the problem and the reason for such sanctions.
While I think that the argument on Forbes is problematic, it may not even be connected to the new Obama sanctions. The sanctions were created by executive order rather than by Congress, so instead of having to try to force an increasingly pig-headed and obstinate House of Representatives to agree with him if he wants to remove the sanctions in the future, Obama may have created a situation where he himself is able to remove them as a bargaining chip with the Iranians.