1996 Lexus LS 400 Misfiring of Engine

I recently had my car tuned up and had new plugs, distributor caps, wiring changed professionally, but it seems the misfiring has got worse. The lexus dealership confirmed that there was misfiring on cylinder # 2, 4 and 7. They said they opened up and inspected and put back everything and reset the codes and test drove it and it ran fine. But when I took the car it started misfiring as soon as I came out of their front gates and it was worse.I have since spoken to the service tech. And they are going to let me know. What do you think is the possible problem. Oh yes and the check engine light flashed and stayed on.