How long does that last, and does it come down to normal on it own? It is supposed to go to around 1500 rpm for a few seconds at start-up. That's called "idle flare-up". If yours is longer and higher, look for a vacuum leak. Check the vacuum hoses and intake manifold gaskets. When the engine is still cold, spray water on the hoses and gaskets. If you see it get sucked in and the engine speed slows down momentarily, you found the leak.