I have a 2016 Trail Edition with 211,000 miles.

For several months now it will idle between 500-700 RPM. I had it tuned up by local Toyota dealer at around 150K. What would fix this?

 

You likely have a vacuum leak somewhere, but it is hard to diagnose over internet.

Find a reputable independent garage and take it there. Stay away from dealerships, they will overcharge you and perform unnecessary repairs.

 

Welcome

 

Dealers, in my opion, only replace suspect malfunctioning parts with new same parts. You pay labor and parts price even if replacement does not provide fix.
For a an evaluation/assessment find a quality independent shop.

 

Nice. Make sure to get your 200k mile sticker from Toyota! I just got mine a couple weeks ago, I'm at 202k on my 2013.

 

In park, In drive, Warm, Cold? Do anything to it lately?

 

Clean the MAF and throttle body. Couple good YouTube videos on it. One is by the Care Care Nut.

 

Welcome

 

What's a "tune up" on a vehicle built after the turn of the century with distributorless ignition? Spark plug replacement and throttle body cleaning? Did the high idle begin right after the dealer service?

 

I would start with cleaning the throttle body. Get some Seafoam spray and a toothbrush and clean the carbon off of it.

 

OP stated he is experiencing 500-700 RPM at idle. Considering normal is around 600-800 after warmup, I wouldn't characterize his as high.

 

^ @SkiSun2405 can try a throttle relearn then:

1. Disconnect negative battery terminal, wait ~30 sec then reconnect negative battery terminal.
2. Turn the ignition key to ON or press the Start button twice, without starting the engine, to let the butterfly valve cycle.
3. Turn the ignition key to OFF or press the Start button again to turn off electrical power.
4. Start engine as normal.