Help, Advice and DIY Tutorials on Volvo's P80 platform cars -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.
it sounds to me that under hard acceleration, your serp belt is slipping and the alternator isnt spinning fast enough so theres a temorary voltage drop, when the rpms go back to slower speeds, the belt grips again.