I would look closely at the ignition. Remove both distributor caps and inspect the caps and rotors. Lexus are also very precise about the routing of the spark plug wires to prevent generation of EMF and to avoid damaging the plug wires by abrasion due to mis routing. Great engine. I am surprised sometimes how they even run as well as they do with a bad cap on one side of the engine.
I looked at it @ work & turns out cyl #5 has a piece of carbon on the valve. Did a cyl balance test & lost compression, rotated crank 45 degrees, used my blow gun, got most of it back. Cust has to decide either to TRY & clean, or get a jasper engine. With 206K miles, not much of a choice. Thanks for the help-Ken