Wordpress PHP If Exists in CSV Update Else Insert

I have been stuck for a little while on this, so am hoping someone can help me.

The principle of what i am trying to achieve is:

Open CSV
Check existing posts if a field with a value from CSV exists.
If it exists then to update it
Else Insert the post

This is the code that i already have, however i most probably have over complicated it.

<?php
function auto_import() {

    global $wpdb; 

    $vehicles = get_posts( array( 'post_type' => 'vehicle', 'numberposts' => -1, 'post_status' => 'any'));

    if (($handle = fopen($_SERVER['DOCUMENT_ROOT'].'vehicles.csv', "r")) !== FALSE) {
        while (($import = fgetcsv($handle, 10000, ",")) !== FALSE) {
            if($row == 1){ $row++; continue; }
            $csv_vrm = $import[4];

            foreach($vehicles as $vehicle) {
                $vrm = get_field('field_5b435f456789j', $vehicle->ID);

                $insert_array = insertVRM($vehicle, $csv_vrm, $vrm, $make, $model, $derivative, $registration);
                $update_array = updateVRM($vehicles, $csv_vrm, $vrm);
            }
            print_r($insert_array);
            print_r($update_array); 
        }
    }
}

function insertVRM($vehicle, $csv_vrm, $vrm, $make, $model, $derivative, $registration) {
   $insert_array = array();

   if(($csv_vrm !== $vrm) || empty($vrm) ) {
      $post_id = wp_insert_post( array(
        'post_title' =>  $vrm,
        'post_name' => uniqid(). '-' . $vrm,
        'post_type' => 'vehicle',
        'post_status' => 'publish',
        'comment_status' => 'closed',
     ));

    update_field('field_5b435f456789j', $registration, $post_id);

    $insert_array[] = $csv_vrm;
    echo "Added " . $csv_vrm . " to insert";
  } 
  return $insert_array;
}

function updateVRM($vehicles, $csv_vrm, $vrm) {
   $update_array = array();

   if($csv_vrm === $vrm) {

    echo 'Both Matched <br/>';
    $update_array[] = $csv_vrm;
    echo "Added " . $csv_vrm . " to update";
}

   return $update_array;
}

The Foreach loop foreach($vehicles as $vehicle) is to loop through the existing posts.

I am open to any suggestions and hope someone can help!