Buy a bag of washing soda.
Tip a quarter of the bag the bag in and run it empty on the hottest wash possible (with no pre rinse)
That should improve it, but always leave the door open when it is empty for ventilation.
Repeat the hot wash with soda regularly.
If that doesn't kill the smell, run it empty with a bit of bleach in, but don't do coloureds in the next wash, just in case.