there is IRS REG 1.121-1(b). it says the sale of vacant land that has been used as part of the principal residence can be excluded only if the land sale occurs within 2 years before or after the sale of the dwelling unit. so the sale of only the land doesn't qualify for any exclusion in your situation. if later you were to ell the residence within 2 years after the land sale you could go back and amend the return for that year to use up part or all of your exemption any remaining exclusion could be used on the home sale. that's because th sale of the house and vacant land are treated as one sale for the exclusion.
