Can't uninstall

The module is currently in the state of being ported, so not all redundant D7 code has been removed yet. But I've removed feeds_tamper.install now. Thanks for reporting!

Hello.

Before seeing this issue here, I faced the same problem on my project.
But I changed the line in /feeds_tamper/feeds_tamper.install:

#variable_del('default_feeds_tamper');
\Drupal::configFactory()->getEditable('default_feeds_tamper')->delete();

Worked for me, but is it better to get rid of the .install file?

Sorry, I'm still a bit rookie on the versions...

@guilmour-asc
In the D8 version of Feeds Tamper the configuration variable is 'default_feeds_tamper' is not used, so there is no need to remove it upon uninstall. Not sure, but doesn't Drupal automatically remove config when uninstalling a module if that config is defined as config schema by the module?

Hey, sup... sorry for the absence.
Well, I'm not sure, too. But certainly my install mustn't be the most stable and secure method, too, hahahaha.
So, this will be a mistery for now.

Thanks for the attention.