Why didn't Goku just IT and save 18 from being absorbed?

Seriously, when Tien was trying to stall for time, why didn't he enter the battlefield, quickly grabbed Tien, then IT near 18 (Obviously Goku can't sense her PL, but he knew she was during the struggle between Sem-Perfect Cell and Tien) While Tien was blasting his way to death, why not grab 18 and 16, IT back to Kami's. Then go back for Tien. Then they could of EASILY finished off Semi-Perfect Cell after their day of training, because he had NO idea where the Z warriors were located.