intermittent rough run

98 Cavalier 2.2 stalling and poor idling.The check engine light will turn on and then it will eventually turn off. I have taken it countless times to the garage and they can never find anything wrong with it. 404 error code is stored and we have replaced/cleaned the EGR valve twice now. The car will be ok for a month or so, then the same symptoms appear. 2 mechanics have told me that if the car is not driven at highway speeds fairly often then it can form carbon deposits and foul up the egr. This car belongs to my mother and i know that it gets on the highway at least once a week. It stalls and drives rough when under 40mph or stopped at a stoplight or intersection. I guess i find it hard to believe that the small amount of city driving she does do is fouling things up so quickly. Any help with this very annoying problem is muchly appreciated.

Anyone?

did you check the air and fuel filters?? maybe the plugs and plug wires as well

Jake...thanx for the reply...all of the usual things such as filters, plugs,etc. have been checked. Every time this happens, the same 404 EGR code is stored. We have taken it to an independent and the dealership to get this figured out, but it is an intermittent thing that of course does not happen when i take it in. Both places have replaced the EGR and it seems ok for 2-3wks., but then the same rough running/stalling will start and stop.

Hey before replacing your next EGR valve, at like $160-$200 a piece try cleaning out the passages to and from the valve,

Had A similar problem with a Dodge Spirit with the 2.5L engine. It never set a CEL. Turned out it was the 02 sensor. Was told that sometimes a faulty 02 sensor won't set the CEL.