feeds importer tamper double importing image
I was having a similar problem using the standard feed tamper modules, so in the end I installed the Feed Tamper PHP module alongside it. Here's some example code I've used to split a string and import multiple values into a field using the Feed Tamper PHP module.  

if (is_array($field)) {
  $value = implode($field);
}
else {
  $value = $field;
}

$field = explode('|', $value);

foreach ($field as $key =&gt; $value) {
  $field[$key] = trim($value);
}

return $field;