Ignition Problem on 2009 Lexus 6 cylinder IS250 w/ 120K miles.

what brand plugs and COP's did you put in it? never seen any codes that tells you to replace parts. why didn't you replace all the plugs at one time?

Mechanic put in Lexus factory parts. I've been reading that it's a good idea to replace all plugs at he same time. I guess the mechanic just responded to the diagnostic and replaced the at fault components. I'm thinking it may be an ignition coil wire issue versus plugs and coils themselves and the diagnostic can't get that specific to wires versus plugs/ coils?

there is no single ignition coil wire like you're thinking,each cylinder has it's own COP (COIL). Denso is OEM for Toyota. DENSO 3473 spark plugs are $11.00 ea. and DENSO COP's 6731309 are $53.00 ea. for a total of $413.00 for 6 coils and 6 plugs.if you had 3 plugs and 1 coil not firing,then the check engine light should have been flashing and you wouldn't have been able to drive it. good luck!