This may be off the wall, but I got it from an independent Volvo tech with years of experience here and in Norway. He says this symptom (which blooms in the Fall each year) can be due to accumulated deposits on the intake valves and in the intake valve area.
The theory is that these deposits soak up a portion of what the ECU intended as extra fuel for cold-running. After a few minutes, as the deposits become saturated and the engine warms a bit, the mixture then becomes adequate for the conditions.
He didn't have a quick fix, except to run some straight Techron or maybe BG44K through the fuel system. More than once probably.
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Bruce Young '93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.
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