My car has had a rough idle. Couldn't figure it out. I changed everything in it, plugs, wires, idle air control valve, cleaned the egr valve, checked for vacuum leaks. Nothing seemed to help. I done some research and read some testimonials about lucas fuel treatment and decided to try some. I put an entire quart in with a quarter tank of fuel and run it until i had to put gas in it. I was surprised with the results, the rough idle stopped and the car starts much easier now. I will be using it in every fill up from now on. Thanks lucas for a great product that actually works.