i think i would rule out the egr as any possible issue,all that would do is cause a high or low idle,if the plunger had a leak it would be a vacum leak and it would cause a high or erratic idle,if the carbon was clogging it,it would bog down,it doesnt sound like thats your issue,your describing it more like a misfire between cylinders,possible defective coil pack,check your coil,then check your rotor for wear,or exxcesive black spotts or carbon build up,also inspect the inside of the dist cap,if its all black and white its from excessive wear and its arcing out the electrodes are not giving you a fulkl spark to ignite the fuel in the cylinder,you may want to replace your cap and rotor and also replace your ignition coil.this is just preventitive maintenance.