Just recently bought a 1998 Lexus LS400 from my uncle at 238,xxx miles (has been passed down and taken good care of by family). Three days ago I was driving home on the interstate with cruise control going about 70 mph (full tank of gas) when the car started to sort of sputter. By sputter, I mean I felt the car jolt forward abruptly, and then feel as if it was slowing down. It kept doing this even out of cruise. Eventually, my RPMS read under 2,000 and I began to lose speed on the interstate. I had to push the pedal all the way to the floor to get any acceleration, this lasted for a few prompt minutes before it no longer worked, and I just consistently lost speed until I was able to pull over to the side of the road. In doing so, I was unable to accelerate anymore. I shut off the car, and restarted it, battery light came on. I was able to take off and make it to my subdivison before it did the same thing, except this time turning over but not starting back up. I tried several times, and the battery never did die. Two days later I try to start it to load it up on a trailer, and it starts fine. I take it to a guy who knows a bit more about cars than I do, and he has it sit and idle for 2-3 hours. The car doesn't shut down. He suggested the possibility of water getting into the gas tank, or possibly needing to replace the fuel pump and/or filter. I drove it back home, and it began doing the same things on the interstate, now it is dead again. So I am completely oblivious when it comes to the subject of cars, does anyone happen to have any speculation or insight, perhaps guidance on what I should be looking at? Car also has an engine light, I tried to check it out and it didn't come up with a code. I'm going to go back out in the morning and try to get it started, I was suggested by an ex Toyota/Lexus mechanic to buy the chemical by HEET to remove water from the gas and put it in.