Suzuki 4WD Club of Victoria

Ok. So every time I start up the g16b on any normal day for it to warm up to temp it idles great on start. After a couple of minutes the idle drops and the engine struggles a bit. After another minute it finds the correct idle again. I always expect it to stall but it's only for that minute or so and always when I start it up just to kick the engine over. It's a stock g16B Vitara engine. No accessories on. Any ideas?
Thanks