Automotive oddity when starting up?

My dad’s ‘04 Toyota Sienna likes to be different whilst starting up. After I stop using the starter, there is a period of about a ½ second to 1 second of silence, though the rev counter climbs to something that varies under 1000 RPMs. After this short period, the engine will either stay very quiet, but become actually audible and stay near 1000 RPMs, or it can surge up to 2500 or even 3000 RPMs. Is this just me not getting used to driving, considering I just started getting behind the wheel, or is this an actual mechanical problem? If it isn’t just me being a noob, is there anything I can do to make it stop, though this is probably harmless?