Hi there Pete

Looks like you are old school like me and yes are having to do a share of reading as well.

The power stage "thingy" is behind the battery on the inner fender well. Looks like black match box on steroids.

It is a current handling electronic relay that powers the ignition coil.
Actually it can be said it turns off the power or breaks the ground that make the secondary windings dump spark towards the spark plugs. Just like the old points but the cam is the CPS via the ICU!

The ECU controls the variances from inputs of the Air Mass Meter (AMM) and oxygen sensor (O2).
A predescribed program, built by lab techies, holds the perimeters for performance and emissions.


The power stage relay, as it is called, does so on the commands from the ICU. The ICU reads the signal from the CPS.

When the key is first turned the ECU powers up and starts a program to run the fuel pumps and then shuts down. This pressurized the fuel rail for quicker starts and better atomization under all conditions.

After this, when the engine is turn over, the CPS signal starts ups the ECU, ICU, and the pumps again!

The weak links are usually the CPS, the Power Stage Relay or the connectors to those.

Being the CPS wiring is frail, over the years of being behind the engine head, it become a suspect.
Being the PSR is behind a sulphuric acid battery, down in a dark damp recluse place, out of sight and out of a maintenance minded person, it becomes a suspect.

Especially the connector, it's ground wiring from that harness.

Since your car is not working while it's colder, it's not a thermal related issue.
It could be sometimes and in that case, it is recommended to service the thermal heat sink paste between its base and the mounting block.

How often to this is not written any where that I know of!

As my own inclination, I think every six years would be plenty. But since this is 2015, you could "notch" the old memory channels for every five years, so it comes out even!
That way that muilti-pin connector always get its "due or do" as well!

Hope this speeds along the learning process!

Phil