Tip 1: UnPack PK4 Files
Go to your Doom 3 installation directoy, then to the folder "Base". There are some .PK4 files there. You have to open each of them with WinRAR and extract their entire contents to the Base directory. You should get duplicates, overwright them. Then delete the old .PK4 files, bettter yet Cut them and paste them somewhere else incase theres problems. BACKUP BACKUP BACKUP.
Tip 2: doom.config
In the Base directory, open doom.config in notepad.
Look for the following pieces and change the numbers to the ones i have shown. If you have alot of ram.
seta image_useCache "1"
seta image_cacheMegs "256"
seta image_cacheMinK "20480"
I'm truly sorry If this is a repost on old news.