The mileage on my 1991 Seville STS, 4.9 engine, 129,000 miles, has dropped dramaticaly. I have changed plugs, plug wires, and air cleaner. This did not help, so I had it scoped at a reputable repair shop. He said it showed a bad EGR valve. Which I replaced. The one I got from the parts store had a different placing of the vacum tube port, I installed it and got no differnce in mileage. What else could it be?
Sep 6, 2007 at 5:47 PM