Normal startup will bring the idle up at first. It should idle down after the auto choke kicks in. The idle up and down while driving can be a resultant of a couple of things. Injector problems, idle control in the cpu, eletronic ignition has a problem, check distributor for cracks and seating. If the engine is heating up and not cooling the thermostat has a problem. Make sure pcv valve is in good shape. Some suggestions without some back up info. Take Care I've experience similar issues on other fuel injected vehicles, thankfully not my civic, but hopefully you can gain from this. After checking every sensor and fuel injector, replacing the ECM (Electronic Control Module) on the advice of a factory trained mechanic (Ford quality for ya!) the answer came to me from a junk car dealer. When the throttle position sensor (located on the throttle body) is worn out (it's circular, usually black outer ring and grey inner, may have a hole in the center) the ECM is not getting the information it requires to control the fuel flow to your injectors and air flow to the whole system. In order to try to calibrate itself it will increase and decrease the air and fuel flow to your engine, since it's not getting it, it just keeps doing it (stupid I know), An engine fault code readout (gotta take it to the dealer for this one) will tell you exactly which sensor has failed in most import cars. TIP! (from a much better trained, older and wiser FORD tech. Sorry Ford fans, but after my repeated run-ins between my Exploder and my mechanic I don't have much faith left) Disconnect the electrical connecter from the Throttle Position Sensor, the ECM will now see that the sensor has completely failed and use it's default settings (Finally!). This should fix your problem in the short term and confirm the sensor failure at the same time. Beware, sometimes you have to reset the computer (accomplished by removing the + connector on the battery, and reconnecting after a couple of minutes) in order to clear the error code that the thing was buggered to begin with, before it will use it's default settings. Sound complicated? Believe it and newer car manufacturers are only adding more sensors so they can gouge you some more. In the electronics world a TPS is known as a varistor, or variable resistor (old style analog volume control), your local radioshack sells them for about $2. That's where the good news ends, you can't use it, the factory (proprietary) TPS sensors will cost you anywhere between $30 - $150, depending on make model and how much the car cost in the first place and o yeah the price of tea in China. good luck buddy, DW Electronics Engineer ANSWER I simple cleaned my throttle body sensor with throttle body aerosol cleaner and it eliminated the up and down idle..Twice this happened and it fixed the problem. You have to hold the 'butterfly' open to get to the sensor which is kinda hard to reach. You may scuff up your knuckles but it worth a try.