foreach $id (keys %id2seq){
        if (-f $id) { print $id." already exists. about to overwrite it\n";}  
        open  my $out_fh, '>', $id or die $!; ##Amendment here
        print $out_fh ($id."\n",$id2seq{$id}, "\n");
        close $out_fh;   ## moved into the foreach loop
    }