Starts and almost stalls

When I start my 02 Trailblazer then engine starts fine but then the rpms go down to about 500 for about 2 seconds then come back to normal. What could be causing this? The car seams fine otherwise.

Could be several things, When was the last time you changed your fuel filter? Throttle body plate could be dirty and sticking.

I have noticed the same at different times, sometimes then, also when just sitting at a light.

Dealer flashed computer or updated software... fixed!