I used Cool White SMD 5050 led light panels on my '98 C70. Lots of light, nice color.

Is it more of a clicking, or a rattling? Does the noise occur when reving the engine in neutral while stationary? Could be lifter tick, which is a sign the oil pickup seals need replacing.

Last I went shopping for lights, I believe Philips made LEDs that were direct replacement for the dome lights, license plate light, and turn signal/ brake lights.

my 850 had a plastic strap when it broke I put two zip ties thru the slots. Canister hooks on a little shelf. My S70 might have the strap and a small bolt helping to secure it to the shelf.

The ECT (coolant temp sensor) and the iAC both act like chokes to richen or not the amount of air and fuel going into the engine when cold. Do you still get the same issue if the car only sits for maybe 20 minutes or so? Fuel pressure should be 40-43 psi when running. This can be checked at the Schr...

Never heard of a gas temp sensor. Might be a diesel thing. I'd be looking at 3 things:

1) IAT valve needing cleaned.
2) Coolant (ECT) sensor is bad so not enriching fuel when cold.
3) Fuel pressure/Relay issue.

Start with the basics.

Neil.