Rpm hunts, randomly

The smell is your catalytic converter the fluctuation of the idling is more likely your O2 sensors.

Thanks Brotherben, car just passed emission test, could it be dirty IAC VALVE?

Wouldn't hurt to clean the IAC, but the smell of rotten eggs is related to the catalytic converter, if it's plugged up exhaust is going to be restricted. But by all means clean the IAC, the throttle body, and look for any vacuum leaks, unmetered air entering the engine can cause a hunting idle RPM. One way to find vacuum leaks is to spritz a tiny amount of starting fluid around the throttle body and hoses with the engine running, if the engine surges then you found a leak.

Thanks gonna try the cheap stuff first