This problem has been around for awhile on my '87 K5 TBI..I pretty much replaced everything and to no avail. I have finally put a tach in along with a few other gauges and now I think I have a little more info on my problem. When the truck is warming up the tach is solid and truck runs great...but after it is heated up and I come to a stop...I can watch the tach fluter...she idles at about 600rpm in gear and the tach will sit there for a few seconds and then jump suddenly with no phisical jump noticed and then fall right back down to normal idle. The truck will also stumble a little during this time. Does anyone have an idea of what this could be? Any help will be great.