The 1999 to 2004 Honda Odyssey’s have a common problem with the Idle surging and causing it to rev up and down and in some cases unable to be driven. The first thing to check is the coolant in the radiator. The Odysseys are known to idle up and down when the coolant gets low. STOP! When checking the coolant make sure the motor is cool before removing the radiator cap. If you try to remove the cap when the motor is running or still hot you can and in most cases will be severely burned due to super hot coolant that is under pressure. In most cases this is the problem, but if you have a check engine light on it may be something a little more difficult to fix. If you can make it to your local auto parts store, they are usually able to plug into your computer to tell you what the issue is when the engine light is on. With a check engine light and the motor reving up and down it is usually a sensor on the bottom of the throttle body called the I.A.C.Valve or sensor. This is also a very common part to replace in this model Odyssey.