$file = New-Object System.IO.StreamReader -Arg "<path to your file>"
$count = 0
$lines = @()
while ($line = $file.ReadLine()) {
    $lines += $line
    $count++
    if ($count % 1000 -eq 0) {
        $lines | Out-File ("splitfile_" + (Get-Date).ToFileTimeUTC() + ".csv")
        $lines = @()
        $count = 0
    }
}
$file.close()