There are number of things causing this problem . It sounds like the engine might be confused about how much gas and air it is getting which might mean it needs a new oxygen sensor (EMISSION) or throttle position sensor. Start with the easy maintenance items like spark plug wires, air filter, and fuel filter if they have not been replaced recently. A bad spark plug wire may only occasionally short out and cause these problems. Try looking under the hood in the dark with the engine running and see if you see any electrical arcing around the spark plug wires or just go ahead and replace them if they are old.
It might just be a clogged fuel line/injector/ or pump, try to put some fuel cleaner in tank the next time you fill it up and see if that helps.
A good way to check your EGR : start the enging, stick your finger under the EGR; you should be able to feel the diaphram. Tap the throttle a few times. If the diaphram moves, it's probably good. Secondly, vacuum. Fill a spray bottle with water and spray all around the intake. If the engine idle changes, the problem is an intake gasket. Your idle will be rough, then smooth out. Check all your vaccum lines too.
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