Software problems of the 1998 Volvo S70

Shortly after purchase car started "bucking/ would feel a lunging forward while driving at high speeds or while idling at stop signs. Complained to dealer was told "they know about the problem" - it is a software problem I was not informed of this prior to purchase. Said Volvo is aware of the problem and their working on it. It is my understanding a computer chip is defective and it is firing fuel into the injectors randomly. I asked if this is dangerous, could this cause a fire, etc. And was told no. I have taken the car in twice and had this problem documented and they have done nothing. It has not improved, only become more frequent. The car surges when at stop signs, it feels like another car has bumped into me. This also occurs when driving at high speeds. I purchase this car "new" and was not advised of this problem. If I had known this I would not have bought car. Also whether the car is in drive or park, this surging occurs. Also a few weeks after I purchased car the o'ring cracked and oil and transaxle grease was leaking out, unbeknownst to me immediatley. When I took it in was advised the ring had not been installed properly at the factory and it had broken. I asked since all that fluid leaked out has any damage been done or would this affect the performance in the future, was advised no. This car is a lemon. Please help me.