One problem related to gas recirculation valve (egr valve) has been reported for the 1998 Chevrolet Astro. The most recently reported issues are listed below.
Plastic pulley on belt tensioner desentegraded causing arm to bust off engine block while traveling on interstate in middle lane. Surprised by loss of brake pedal while pulling over to emergency lane in heavy traffic! glad my wife was not driving the van at this time. My opinion is that not only is this a cheap part , but possibly dangerous in certain conditions. Not to mention stranded 40 miles from home.