Hi,

Welcome to Brickboard!

You asked:
"Critical thing here is that neither problem occurs once the engine is warmed up - accelerating and idling both return to normal. What are some causes for poor idling and acceleration on a cold engine?"

Answer:
Yes. Firstly you could say the ignition system is the most critical one working during start. Delivering such very high voltages from the word GO!

Check your spark plugs, ignition cables, rotor and distributor cap. I would just replace them all in my car about every 5 years time. If you still have any original parts then its long overdue.

Secondly check if your engine is equipped with cold start injector (sorry, not familiar with 1983 Volvo engines). Throw in some fuel injector cleaner such as 3M, Techron or STP obtained from parts store. Not heard of any injector failure so far but some do need cleaning from time to time (this depends on what quality fuel being used).

Hope these helps,
Amarin.