Just some shower thoughts that has been bugging me for a while now.

1)
Does anyone know in a auto, the zf8hp to be specific, when in motion, does shifting to N and then shifting back to D at speed causes any significant stress on the drive train? How about in the same scenario, revving it up and shifting back to D before the rev drops back down, is there any more stress to be had?

The zf requires you to engage the brake at low speed to shift from N to D, but not when you are at speed.

2)
Is there any difference idling at 1st or 2nd gear? I use paddles all the time, and notice that idling is way smoother on 1st or N, and rougher on 2nd. Which gear does it default to while in D at idle? Also, what causes it to jerk prominently shifting from 2nd to 1st, but not any other shift?

3)
Unrelated to transmission, does our pop and crackle increase fuel consumption since it's dumbing extra fuels into the engine when you are not demanding throttle, or a better question is, how much?

 

1) Automatic transmissions aren't my specialty (my F-Type is only the second car I've ever had without a third pedal), but I'd expect that - within reason - there wouldn't be an issue coming in/out of neutral into drive - even with some rev.
2) There isn't anything particularly different about idling while in 1st vs 2nd. "D" defaults to 2nd gear; you can only get to 1st using the paddles or shifter. The difference in effect downshifting into 1st vs other gears is primarily due the difference in gear ratios combined with the speed from which you're making the change. There could also be some programing effect on how dynamically the gear changes are made.
3) Yes, you're dumping fuel. The exact amount depends on how and how often you engage the effect (paddles on upshifts when keeping the throttle engaged, chronically downshifting through the gears, etc). But, it's not THAT much (maybe a fraction of a mpg), so enjoy yourself.

 

Ideally, if you're gonna pop it into neutral while driving, give it a blip when going back to drive. A bit of make-shift rev matching so you don't get that lurch and put less shock on the drive train.