Then it is a states right issue

23 States Sue Trump Administration In Escalating Battle Over Emissions Standards

23 states did not file a friend of the court brief, they sue because they lost something they had a right to.  There is no other constitutional way to interpret this.

What dis Congress say, in the law:

The move "exceeds NHTSA's authority, contravenes Congressional intent, and is arbitrary and capricious, and because NHTSA has failed to conduct the analysis required under the National Environmental Policy Act," states the complaint filed in the U.S. District Court for the District of Columbia.
The National Environmental Policy Act, signed into law in 1970, is considered a kind of "national charter" for regulating the protection of the environment.

The claim is that Congress authorized the California exemption.  Then the 23 states have no basis except to claim the environmental catch all.  But the 23 other states have no tort claim under that law since they themselves have allowed emissions higher than California, without environmental review. The 23 stupid state attorney generals are suing for the right to have higher emissions than California, any of those AG get the paradox? Anyone in the Supremes notice?

What we have is the accumulated history of Sotomayorism over the decades. The court system is lost in the labryinth of bureaucratic administration rules, way beyond any reasonable separation of powers. The Supremes have no way out, not with Roberts, Thomas, Sotomayor and Kragan. The courts will never become unjammed, we are headed to failed Hispanic state.

Most of these lawsuits are completely unrelated to Constitutional issues, they are about idiots in Congress in way over their head in micro-managing, thus failing to resolve these disputes, or let the executive resolve them.