This doesnt really bother me but I was wondering what causes my car to go "idle hunting". When I pull the choke out to start it up when she's cold, it will start up straight away, idle nicely at 1000 for about 10sec then drop to about 600 and bounce around +/- 200rpm.

Sounds like a drag car idling which is pretty cool...except for the masses of unburnt fuel coming from the zorst. Its a great trick at the lights to pull out the choke and give it a bit of a rev, sounds like a big old-school hemi, scares the hell out of the P-plate ricers in their mummy's economy 4bangers.

I know its caused by having the choke out but does anyone know why it jumps around instead of staying at a constant rpm?

Nobody?

My EFI'll hunt occasionally, but only over about a 100rpm range.

Why do you have a manual choke?

i was led to believe all magnas had auto choke... especially considering mine is a leaded TM and has an auto choke...