Grand Prix shaking

Hey got a question for you all. I have a 1994 pontiac grand prix, 3.1 l v6 engine, I posted on here a while ago about shaking problems, it woudl shake really bad while driving. I took it to dealer and had a fuel injector replaced and all six spark plugs, on two of the spark plugs the electrode was completly gone. My car burns oil really bad, I have to add 2 quarts about every 1000 miles on a pretty consistent basis. It's been maybe three months now and the car has been running perfect, but the other day I went to start it and once it gets to around 1000 rpm it starts shaking very hard. It will continue to shake until I put it in gear, and then it will not shake as bad and as soon as I am driving for a couple minutes it wont' shake at all anymore. It only happens when the car is sitting for long periods of time, mainly when I go to start the car to go to work and after I get off work. If I am driving it and have to make a stop and turn the car off, if I turn it back on it won't shake at all really. I'm starting to hear some of that pinging noises from my engine too. Do you think maybe the oil is leaking somewhere around the spark plugs and is making them faulty? Any ideas at all woudl be helpful thanks.