06 m35x wants to kill when starting ????????

[sporn32]

i have a 06 m35x after it sits for 45 minutes to 1 hour, hit the start ignition starts up but the revs real low like it wants to kill, then it comes out of it and revs to normal, the car could sit for 8 hours or 5 minutes seems like it only has this problem between 45 minutes to 1 hour brought the car in twice cant figure out whats wrong. any ideas out there.

any help would be great, thanks