I recently switched out my heated O2 sensers and the check engine light had gone out. it is back on now and I pulled the codes from the ECU. it is comig back as as the EGR system. the car seems to idle just fine, but the engine seems to vibrate exsessively between 1500 and 2000 rpm. the car is a 1993 90s with the 12 valve v6. every thing seems to be running well enough. is this something i need to get fixed imeadiately, or can it wait? accelaration is as satisfactory as it ever was. the car currently has just under 130k. I have heard a vaccum leak could cause this. how would I go about finding and or fixing something like this. Any help would be greatly appreciated.