I have an '89 Skylark, 2.5l with 193K on it and I am having the check engine light come on and go off it seems after periods of idling for awhile. I think the OBDI code was 21 or 23 (EGR recirculation error, I believe). The EGR valve has been replaced and is vacuum controlled by a line going from it back to the rear of the throttle body. I made sure I got the right one since some are controlled by negative pressures and some by positive. Anyone have any ideas? Thanks.