AVR-Chat

Hi,
This is my first post here.So i hope im being relevant.

I,m using the ATmega 16L chip on one of my battery powered robots.I am 
using the Pony 2000 serial programmer to download the codes on the 
chip.Here is the problem i'm facing:

I'm using the on chip RC oscillator at 1MHz to clock the chip.To test 
the speed of my bot i wrote a delay routine of 5 seconds after which 
the bot stops so that i can measure the distance on the ground 
travelled.Now the problem is that i'm getting erratic delays.Sometimes 
i get a delay of 5 s while sometimes i get a delay which is much 
longer.Plz Help!!

If u want any other details on my ckt. mail me at 
neosdomain4u@yahoo.co.in