May have nothing to do with autocomplete. Did you verify the /tmp directory is present and writable? Do this command:
ls -ld /tmp
Does this command output the following (the italicized parts will vary on your system):
drwxrwxrwt 25 root root 16384 Oct 23 11:15 /tmp
The important output is the first and the last columns. If it says that there is no such file or directory, then this is your problem. Create it with this command:
sudo mkdir /tmp
sudo chmod a+w /tmp
If there are dashes in the first column, then this is your problem, fix with this command:
sudo chmod a+rxw /tmp
If any of these commands fail, then I think something wrong with your file system.