Can I sue the city for selectively enforcing zoning laws?

You may use the courts to enforce some right you have that has been violated. This dispute sounds like a misunderstanding of the zoning code which you should point out to the inspectors. Involve your elected official(s) to work toward a satisfactory outcome.

Good luck.

Check with a lawyer in your locale to discuss more of the details.

You might find my Legal Guide helpful "Ethics: Yes I Need a Lawyer!"

http://www.avvo.com/legal-guides/ugc/ethics-yes-i-need-a-lawyer

Good luck to you.

God bless.

NOTE: This answer is made available by the out-of-state lawyer for educational purposes only. By using or participating in this site you understand that there is no attorney client privilege between you and the attorney responding. This site should not be used as a substitute for competent legal advice from a licensed professional attorney that practices in the subject practice discipline and with whom you have an attorney client relationship along with all the privileges that relationship provides. The law changes frequently and varies from jurisdiction to jurisdiction. The information and materials provided are general in nature, and may not apply to a specific factual or legal circumstance described in the question.

I agree with Mr Brinkmeier; you should speak with the inspectors about the enforcement of the law. Filing suit against the city would be expensive and time consuming so it is in your best interest to try and work this out amicably.