I bought this 2001 Buick LeSabre Limited about a month and a half ago. When I bought it the previous owner said it was using coolant and oil. I changed the LIM gaskets(updated design) and upper intake plenum. While I had everything apart I cleaned the throttle body very well. I don't think that they changed the oil too often as I found sludge when I changed the front valve cover gasket. I ran a hanger wire down the oil return holes to ensure they were clear. The coolant level is staying constant but it still seems to be using too much oil. It doesn't burn it constantly but only after about a half hour of driving. By that time I am in stop and go traffic in Brooklyn and it always blows a cloud of blue smoke when I take off from a stoplight. It will only do it if I have been idling for more than 10 seconds so it doesn't do it from just a brief stop at a stop sign. I have changed spark plugs(it seemed like the originals were in there as the nuts were rusty and they were AC Delco) with NGK TR55. The original plugs showed no signs of fouling. The engine has 139k on it and is very reliable, has decent power and gets good gas mileage but this smoking is embarrassing...Any ideas on what could be causing this???