I search on the forum and don't think I found exactly the same problem.

my car generally run fine, but i have the limp mode light to turn on for
no reason.

This happened to me 4 times now in the past month.
1 time the idle became rough, then check engine light come on, code 3091. (high pressure fuel pump issue)

I read and cleared the code at autozone,
then I brought it to the dealer, and they couldn't find anything, and since
the code is clear, they wouldn't do anything. The engine code hasn't come back since, just limp mode.

All 4 times happen when it was idling, 2 times at red lights, 2 times I was
parked and setting up GPS...

On all 4 times, I just shut off the car and restart, everything is fine.

what could cause this?

 

Sounds like the fuel pump. They have been a problem for some time.

 

High pressure fuel pump. In my experience, when it is failing, it will sometimes function correctly after a restart. It will eventually (soon) fail completely and the car will barely run. It's not a hard job, so I'd replace it as soon as possible.

 

If you go into limp mode there's always a reason, did you think deleting the code would make the problem go away? If you had not cleared the code for the HPFP Mini would have installed a new one right then and there. Now you'll have to wait until it happens again and you might even be stranded somewhere.

 

It's probably bored, try revving it up, ya know, to get it excited.