So you had brand new tires put on the car recently and have them balance and did not get an alignment or fix a bad suspension? Well they won't be new for long. That oil additive a lot of times is a thick gooey substance that sticks to everything and supposedly makes things work better by adding content to the walls of the cylinders. People are suggesting using transmission fluid because it's thinner and can wash that crap out of there. my suggestion is just to change the oil get in it get any of that crap out of there with some good fresh clean oil and I say this because you said the motor sat outside the car for a year.