Here is something I picked up from this web site:
SmogSite It says:
EGR Problems: Either it doesn't work when it should, or it does work when it shouldn't. Or it doesn't work the right amount.
The EGR may not work because vacuum lines crack, fall off, or are misrouted. Or the big EGR diaphragms leak away the vacuum, or the transducer won't close off it's vacuum leak so the vacuum signal doesn't get to the EGR valve. The EGR valve may be corroded shut, or maybe even the EGR passage is plugged up so exhaust gas can't flow to the valve. Or maybe the computer solenoid goes bad and won't turn on the EGR vacuum or valve anymore. All these will stop the EGR from working.
Maybe the EGR sensor on top of the EGR gets a glitch in it, so the computer doesn't know exactly how open the valve is. It gets all confused and either turns the valve on too much or not enough erratically. The customer experiences some hesitation or real bucking. Part of this is because the computer is advancing the ignition timing more with the EGR flowing, to try to give us more fuel mileage and power with the EGR on. Then when it doesn't know the EGR position exactly, this computerized timing advance jumps all around.
The EGR only starts being used when in closed loop and at part-throttle operation - not WOT or open loop, if my memory serves me correctly...? This may be an avenue or not but I thought I would post it to spur thought. Any thoughts on this at all? Thanks.
