I've never heard of coolant going to a throttle body.
Obviously the designers must have had a reason for that.
Seems they want it at engine temp for some reason?
anybody know the actual reason?
It's common on other cars. The stated reason is to keep the throttle from potentially freezing/sticking in very cold weather, which always seemed very unlikely to me given that the engine bay and block are 100+ degrees even in the coldest conditions.
I asked chatgpt which agreed this seemed unlikely, but brought up the fact that at low throttle you have a Venturi effect (increased airspeed, decreased pressure, rapid cooling). So in theory if you were driving in cold weather, with high humidity and an engine that hadn't fully warmed up, at low throttle, icing could happen.
I asked it to quantify that risk, vs. the costs the system (development, loss in efficiency from warming intake air, potential reliability/leak concerns) and it reckoned that the systems were developed long ago so R&D is minimal, and they probably only raise intake temps by 5-15 degrees, which wouldn't translate to measurable fuel economy and would only cost a couple percent of power at full throttle.
So the risk of icing is low but nonzero, and the costs the system are low enough to justify. When I pushed it to guesstimate mileage improvements, it reckoned a 10 degree drop in intake temp (say 120 to 110) would increase air density 1.6%, so 1.6% more power at the same throttle, and maybe 1% better mileage once throttle was reduced appropriately.
Edit: as another example, the Z32 300ZX runs coolant lines underneath its relatively massive intake manifold. Guys remove them for reliability/leak prevention (8 connection points!), and because it significantly simplifies and speeds up future intake manifold removal: