I know this doesn't deal with my k5 but it may be relevent to you guys with fuel injection. On my 95 slowmaro I have a problem with the engine smoking (from the tailpipe) only when it idles for a few minutes when hot. It doesn't smoke when starting up but once it smokes and I take off it goes away then when I slow down it takes a few minutes then it smokes till you get going. My engine guru friend said it was the rings (I thought it was valve seals but not smoking when starting up puzzled me). He asked if it had overheated before yes it was he said if the rings get over heated they will loose tension and while going down the road the O2 sensor things the motor is running rich then leans out so it turns the burning oil into ash when at an idle the engine can only lean so much to keep it running hense the smoke. He said this happened to his 86 chevy p/u with a 350 and tbi. He said he finally figured it out when his $30,000 bass boat was covered in oil ash the first time he towed it. Just thought I'd pass it along...(man I wish it were the valve seals!) Blood, sweat, tears, and lots of money is what keeps the k5 alive.