open guerilla and open the actor variet file your
going to use for your ai.scroll down to the grenades section,there are a few settings for the ai here...
grenade velocity:this needs to be set to a positve number,so for marines i used 9,for elites i
reckon your should maybe use 10 to 12.
grenade ranges:this is like the distance for which the ai will throw a grenade.
grenade chance:this is how likely the chance will be that the ai will throw a grenade.
grenade check time:this is how often the ai will check to throw a grenade.
encounter grenade timeout:this is set to control how often they will throw a grenade.
this is how mine were set up for testing it...
http://img69.imageshack.us/img69/9295/aigrenadesettings.jpg