As if the auto industry didn’t have enough problems, Iowa Democrat Tom Harkin has a bill pending in the Senate that would require 90 percent of all vehicles to run on a blend of mostly ethanol by the 2016 model year.

The proposal is bad for automakers and bad for the economy.

It is only natural for a corn-state senator to seek a rule that almost all autos run on almost all ethanol. But there’s no reason the plan should be taken seriously.

It would require a major investment in infrastructure. Harkin’s bill would require most vehicles to operate on an E85 blend, or 85 percent ethanol. Most gas stations and vehicles are designed to deliver and run on E10, or a 10 percent ethanol blend, and many older cars seem to have a problem with ethanol. Shane Karr, an official of the Alliance of Automobile Manufacturers, notes than only 2 percent of gas stations currently sell E85.

Karr estimated that Harkin’s bill would impose a new cost of $2 billion to make all of their vehicles flex-fuel ready to accept a mostly ethanol-based fuel — not to mention the cost of retrofitting that would be required on all of the nation’s gas stations.

And for what purpose, aside from providing a huge demand for Iowa corn? The manufacturing of ethanol consumes at least, if not more, energy than the refining of oil into gasoline. It is not as efficient in moving vehicles as gasoline and its use of corn drives up food prices.

Harkin has done his duty for his constituents by introducing the bill. His colleagues should do their duty by their constituents by declining to adopt it.