Follow Up
Thanks for all your valuable advice. In the end it turned out to be the THROTTLE POSITION SENSOR.
But let me tell the whole story. Based upon the advice of a few experienced Honda mechanics, this seems to be the way to go.
1. 
Start with a vacuum leak, like a knocked off vacuum hose. No solution?
If the engine is COLD when the problem occurs, 2. 
continue with the IDLE AIR VALVE -- clean it, test it, or replace it. While you are at it, test the FAST IDLE THERMO VALVE also, if your model has one. Still unstable?
If the engine is WARM when the up and down happens, 3. 
next try the THOTTLE POSITION SENSOR on the throttle body. (You can not usually buy the sensor alone, but the whole throttle body only, so buying it used saves a lot!) Still no luck?
4. 
h: Test or replace the MAP sensor, located in a control box often. Still doing the rollercoaster?
5. 
Clean out the EGR valve or replace it. Still stubborn?
6. Look at the advice given by all the contributors to this thread or take out a loan and head for a dealership garage.
Hope all this helps. .
Last edited by gulfview; Oct 27, 2006 at 04:04 PM.