When did you have it serviced last? Opti's need a new set of plugs about every year under normal use. Sounds like a fouled plug, ignition coil or coil driver, possibly a TPS failure or an exhaust divider plate gasket. But from the cutting out you describe, sounds like ignition or injector. Or, an electric fuel pump running weak. If a cyl is missing at idle on an opti, you may never know it as the computer compensates for that by maintaining steady rpm's. I will be in the shop tomorrow. But, I don't have a DDT to read codes yet. But I can probably figure it out fairly quick old school. But, if you do need a DDT, I know where to send you to get it checked out pretty fast. PM me and let me know. I'll be fishing Wed and then the heavy rain rolls in.