Nissan Repair: Nissan Sentra, nissan sentra, egr valve

Question
I have a Nissan 1997 Sentra. 1.6L automatic, 122,000 miles, uses no oil and I maintain regularly that has the service engine soon light comes on, stays on and then goes off after some time. In the last year it has been on about 8 times. I have asked many people what the code means and  can not get an answer that corrects the problem. The code is always 400 "Flow Malfunction". I change all filters, fluids, plugs, etc. myself. As of late the car hesitates every now and then from a cold start and then goes on with no problem. This problem has not affected gas mileage. Any answers???

Answer
Dan,

The code means that the EGR is not flowing properly.  That is, the EGR valve could be defective or the path could be blocked with crud.  Since you say it comes on and goes off it would lead me to think the valve could be removed and the port cleaned and then reinstall it and clear the code.  If the EGR valve stayed off the seat at idle the car would idle badly.  If it is just broke it will not hurt your mileage.  But, if you have to pass smog you will need it corrected.