I have an 03 ES300 that has a steady hesitation through all gears. 

No OBD2 codes

In open loop the car runs great.

Closed loop it starts to have a steady "surge" upon acceleration.  With the AC on it is more pronounced.  I unplugged an A/F sensor to keep in open loop for testing performance.  Runs great in open loop.

Both front A/F ratio sensors have been replaced within the last 20k miles.  Denso sensors were used.

Throttle body and EGR removed and fully cleaned.  Reinstalled with OEM gaskets.

Plugs replaced with Denso Iridium

MAF sensor cleaned

Air filter replaced

Both air intake boots were old, so those have been replaced

All vacuum hoses replaced.  Zero indication of any vacuum leak.

VSV switches tested and fully operational. 

Ran a couple tanks of high octane with Berrymans cleaner.

I have a feeling its got to be one of the sensors in closed loop mode is bad but not throwing a check engine light. 

Or perhaps its a bad cat. 

I'm at a loss at this point and thinking of taking it to my local Japanese car specialist to diagnose.  They are excellent, but very pricey. 

Any ideas anyone?

Car has 149k and has been well maintained throughout its life.  Oil changes, timing belt 39k ago, new radiator and coolant flush.  Trans fluid changes, brakes, tires, etc.. 

I hate to part ways because its been in the family its whole life and is extremely clean.

Thanks for the help.