Rpm Dropping Almost Stalling?

[RB25PWR]

Whenever I come to a set of lights I down shift then put it into neutral while braking, then my RPM drops to 500 sometimes 450 then back up to 650. On the odd occasion the car stalls, what might be causing this? Not sure if it matters but it never does this while really cold, (like when it's still idling at 1100rpm).

Also my engine temp gauge never ever sits at half way, do I just need to get a new thermostat? It usually sits in between half way and cold.

One more problem. Occasionally when at idle I can hear a ticking sort of sound (can only hear it at idle)...

I just did an oil change + oil filter change with Motul 8100 5w 40... but I'm pretty sure it was ticking occasionally before then too.

Thanks for reading.

[Socrates]

Not sure if same for you, but my temp sensor was rusted a lot so it was showing lower temps than normal and would never go over half way.

How old is your radiator water?

Last flush?

As for ticking noise, I can only comment as its happening with my engine currently and I'm not too familiar with RB engines but it could be tappet adjustment (valve clearances) that are out by a little bit.

Good luck.