I've been searching this issue and haven't found what I'm looking for.

I have a 2003 Lexus Gs300 with 189k on it. Spark plugs done about 3k miles ago.

2 weeks ago my CEL blinked at me on the way to work. Leaving work it went solid and the car started to idle really rough. When I got home I pulled a P0306 Code. Cylinder 6 misfire. So, I swapped the very last coil pack, and the very first coil pack. This way I didn't have to take the intake manifold off. I drove it with no issues for 2 weeks. No CEL either.

Today the CEL flashed again and then went solid. It started to drive very rough like before. I pulled the code: P0304 Cylinder 4 misfire.

So, is it that first coil pack that came from the rear position?

any help is appreciated.

 

You have moisture in your tank. Happened to me back in February. Now this what I did & it worked. I have no issues, 0 issues. What ever gas u have try to burn it out. Let the car idle or drive it around. Don't worry it'll burn fast since the car is running harder to stay idle. Get you a gallon of lacquer thinner. Any auto parts store or home improvement store has it. (Auto zone, Napa, advance auto, home depot, Lowe's). Pour the entire gallon in your tank, then fill the tank to the half line with premium gas. Drive around on that mixture until it empty. Then refill with premium gas. The thinner will absorb the the moisture in the tank. The light will go out and the rough idle will stop.

 

Also change that 1bad coil pack. I also removed the air inlet form the throttle. & with the car off I use a small brush with carburetor cleaner spray. Sprayed the carb & use the brush to break up the carbon deposit & carefully opened the butterfly and cleaned that out. Note: car will run right after you do this for a few seconds