308 Cold Idle Question

Check you Air Bipass valve that I think is under the water expansion tank, make sure the electrical and the vacuum hose are installed properly and tight.

 

The "G" light coming "on" if the RPM drops to ~500 RPM is just a normal result from the too low enigne speed.

Not having the cats nor air injection has no effect on the cold-running vs warm-running RPM of your US version? 308-2Vi, and it could get worse as the temperature at cold start goes lower (but it seems like you've got a problem that needs to be addressed anyway).

It is true that many US 308-2Vi have had the cold start air valve disabled (because the ~3000 RPM at cold start-up is a bit extreme -- but I favor adding an orifice restriction in the cold start valve air path to drop the cold start RPM to maybe 2000~2200 RPM rather than disabling it completely) -- without it, a (stock US) 308-2Vi will run very rich at cold start-up, but should still run/idle OK-ish when cold.

Here's a brief overview of how a US 308-2Vi runs cold vs warm for both a stock system and a system where the cold start air valve has been disabled:

Stock US 308-2Vi
Cold
1. The AAV (a thermomechanical device) is partially open and allows some extra air into the intake tract.
2. The Thermoswitch in coolant tank is "open" -- leaves the electrovalve controlling cold start air valve "off" -- with the electrovalve "off", vacuum from the intake manifold is connected to the cold start air valve -- with vacuum applied, the cold start valve's air path is open and allows more extra air into the intake tract.
3. The Warm-up Regulator (another thermomechanical gizmo) is more open which allows more fuel to leak back into the fuel tank -- this lowers the control fuel pressure -- which allows the Plunger inside the Fuel Distributor to move farther for the same amount of airflow -- which opens more of the fuel delivery slits -- which adds richness.
Summary: The AAV and the cold start air valve are both allowing extra air to enter the engine. At the same time the WUR is causing extra fuel to be added by the Fuel Distributor so the RPM and A/F ratio when cold is where the designers intended (somewhat high to heat up the cats quickly).

Warm
1. The AAV has been heated by the engine itself and its internal +12V heater -- this closes the AAV so no extra air enters the engine.
2. The Thermoswitch in coolant tank is "closed" -- this energizes the electrovalve controlling cold start air valve with +12V -- with the electrovalve "on", vacuum from the intake manifold is removed from the cold start air valve -- with no vacuum applied, the cold start air valve is closed and no extra air enters the engine.
3. The Warm-up Regulator has been heated by the engine itself and its internal +12V heater and is more "closed" allowing less fuel to leak back into the fuel tank -- this raises the control fuel pressure -- which reduces the plunger motion inside the FD for a given airflow -- which reduces the idle fuel delivery to the amount set by the Mechanic when previously adjusted at warm idle.
Summary: The AAV and the cold start air valve are both closed. The WUR + FD is delivering the amount of fuel set by the Mechanic to achieve a 1000 RPM warm idle and the proper A/F ratio.

When the cold start air valve is disabled, warm-running is completely unaffected, but the cold-running will be very rich (because the fuel system is still delivering extra fuel in anticipation of the extra air) -- very bad for the cats (which I realize that you don't have). The cold idle RPM will be reduced (maybe 1000~1500 RPM), and others report, that even running rich, it still runs/idle OK. If yours is a US version with the cold start air valve disabled, and it runs/idles at 1000 RPM perfectly when warm -- I'd put the highest probability on it being some sort of WUR problem, but check the AAV operation too (and if your warm-running is iffy you should have the system measured/tweaked up anyway). HTH and good luck...