My 03 has it. If its below 32, after 2 mins of idle it bumps up. I have driven down the road 5 or 6 miles and I parked it idling for a few mins and it jumped back up again. I dont know what temp the idle quits kicking in after the truck is warming up.

 

Perfectly normal.

 

Use your triple dog to enable it. There is an option on it that say High Idle.

 

It doesn't. It will idle up and down constantly when the intake air temp drops below a certain point, even if you are at full coolant temp. ECU's attempt to stop wet stacking and keep the combustion temps up.

 

It is standard on all trucks, not even a way to turn it off.

its based on coolant temp as well... If the coolant is above 160* it will not fast idle..

~32*F after 2 minutes rpms ramp up to 1,000 (until stopped or coolant reaches 160*F)
~15*F immediately rpms ramp up to 1,000 (until stopped or coolant reaches 160*F)

 

The feature that has to be enabled is the manually controlled high idle that is activated/controlled using the cruise control buttons. What is being discussed here is the automatic high idle feature that is activated by cold temps. Don't know when it first became a feature, but my '04 has both.