I did see "on this forum" a suggestion to
simply
A. pull both relays next to the overflow tank engine bay RHS when looking forward through windscreen and
swap them.
I did this and one other thing which was to
B. remove and thoroughly clean the coolant temperature sensor, replace it and ensure the correct harness wire is installed to it.

This may well fix most problems to do with cold start, fuel run injectors, and also make some great soup.
It may stop the aircon condensor aux fan.
This is not a major problem (unless you are in the SAHARA) , but must be rectified. Car is driveable without damaging .
You can soak the wire ends in white vinegar overnight to tidy up any oxidation.
You may need to buy a new relay from IPD. Buy two.
IPD will assist with the wiring colours arrangement I'm sure.

On doing these two things my car started "pop" and does so every time.
Nothing else I did fixed the problem of no-start -
these things I did previously include
(in no particular order)

• replace throttle position sensor, (happened to have a new one)
• replace the Idle Air Controller (not new!),
• replace the MAF with another (not new!),
• replace the cold start injector, (not yet done the O2Sensor replacement but have a new replacement part),
• ensuring airtight air flow for crankcase ventilation pipes,
  • to verify airtight in the tube connected to the MAF,
    • hold the air tube to view the inside of the end with 2 hose connectors,
    • shine a bright torch on the outside and at the connector points while looking directly onto the inside of the connector,
    • any air leak will be seen on the inside as a torch brightness surrounding the connection point. (hopefully you will be in a slightly dark space)
    • If torch brightness is there the hose needs to be replaced or the gap fixed to make it air tight.
    • Any leak will cause problems.
• replace fuel pressure unit (non-electrical) (not new!),
• replaced distributor cap and leads and coil (all new),
• NGK plugs,
• tore out 4 (four) patches of hair,
• replaced external fuel pump and filter (both new) ,.

Do NOT forget to check Codes (see https://www.troublecodes.net/volvo/) displayed by the box up next to the wiper motor directly inside the engine bay in front of the driver.
Good idea to use the rubber grease on the connecting point for any two rubber hoses.
It makes it a breeze to fit, don't forget to tighten with the steel hose clamps thingo.

Ensure ALL connections are clean and test after EACH replacement part is installed.

I do not expect a single problem from this motor for 100,000 miles (or 160,000 kilometres here in my home region)
I also did the cam belt, seals, and tensioner roller, replaced fan belts and set correct tension
***: if you have instrument panel problems like

• dead odo,
• speedo wonky/dead) then

1. tightening your alternator belt to a correct measure.
2. Also check that a correct voltage of 14V(?) { ? AMPS ? } is output from Alternator.

ALL These things improved fuel consumption by 30+% over what was there previously.
Motor is a smooth and purring like a tight, strung, viola.