The TPS needs to b change
Your car is more than likely still under warranty, and you need to take it back to the dealer for them to look at it.
It's located on the Throttle Body and has an electrical connector plugged into it. It can be removed and cleaned with throttle body cleaner if you are having idle/idling, stalling, or surging problems. It is a cylinder shape with a plunger on the working end.
the water was surging over the rocks
It is important to know the causes of problems in a vehicle. A surging idle can be cause by a bad o2 sensor, bad fuel pump, or a computer starting to go bad.
Your check engine light will be on and you will feel bucking or jerking while you are accelerating. You will also have an idle surging, sudden stalling of the engine, and a sudden surge in speed while driving on the highway.
Converters get hot when they operate and this is normal. However a partially clogged converter will get excessively hot and my even turn red. This will cause a loss of power, stalling, and surging.
a coolant temperature sensor:can cause hard starting,stalling,blacksmoke from tailpipe,hesatation,rough idle,surging,cold engine warm up problems,poor fuel economy, the sensor sends a signal to computer!! fuel mixture and ignition timing are also affected by coolant sensor.
From the sounds of it, the AIC Valve (Air Idle Control Valve) is on the outs!!! Surging is usually the giveaway of this .... stalling is the other. Now .... with that said, there are other reasons for this as well. There could be water in the fuel or you may have a vacuum leak or a few other problems. I would have to suspect the AIC Valve is the culprit though as it's a very common part that fails on many of today's fuel injected cars. Good Luck.
My Haynes repair manual shows : It senses throttle movement and position , then transmits a voltage signal to the PCM . This signal enables the PCM to determine when the throttle is closed , in a cruise position , or wide open . A defective TPS can cause surging , stalling , rough idle and other driveability problems because the PCM thinks the throttle is moving when it is not .
Surging Seas - 1924 was released on: USA: 1 May 1924
The most common cause for surging is a vacuum leak