92 honda accord with fault code 12

my 92 honda accord gives me a fault code of 12 and the check engine light comes on. The book says to check the EGR and hoses, but wha am I looking for???? Also after about 5 minutes of idling it starts to sparatically idle. Any ideas on what the cause here....
would like to help but need more info like what engine, any recent repairs ,mileage , carb or injected..ect let us know ..k ..........Todd
soldier; Pardon my jumping in here. Code 12 is EGR system. From the symptoms you describe, it could be that the EGR is stuck partially open. Sometimes a piece of carbon will get stuck between the pintle and seat. This will usually happen, or at least be noticed, on deceleration from above 40mph. You can remove the EGR valve and visually inspect the pintle area. You'll see two passages. One with the pintle, and the other an open port. You shouldn't be able to blow through the two. Or, you can pour water in one and see if it leaks through. Sometimes, you can use carb cleaner and clean the pintle/seat. The vacuum line going to the EGR valve should NOT have vacuum to it at idle. If it does, then there is a problem with the EGR sensor/switch. If you have a vacuum pump, you can apply 14hg to the valve. The engine should at least stumble, if not die. If no change, the valve either isn't opening at all, or it's already stuck in the open position. The fuel injection will see this as extra air and command more fuel to try and compensate. But, don't run out and buy and EGR valve, yet. Let's make sure it's the valve, first.