2016 Honda CR-V spikes RPM from 1000+ to 3000+ when turning left to descend a small hill, every time. Foot is not on the accelerator, just coasting down hill. Stomping on the gas pedal will return the RPM below 1300, but I do not want accelerate down hill with a sharp turn at the bottom of the hill. Why the spike in RPM?

 

It is Honda's grade logic control system.

"All Honda automatic transmissions incorporate the Grade Logic Control System, which uses a powertrain control module (PCM) that is programmed to select appropriate shift points from stored PCM "shift maps." By controlling the engagement of 3rd, 4th and 5th gears when driving uphill or downhill (2nd gear as well on the Civic and CR-V), Grade Logic Control improves driving comfort and control.

Many conventional automatic transmissions use a single shift map based on throttle position and map sensor (to determine engine load) and a speed sensor (to determine road speed). While shift points from these two inputs are correct most of the time, there are situations that can "fool" its computer. For example, when driving up a long hill, the driver presses on the accelerator to compensate for slowing. The car downshifts to a lower gear and speeds up in response to increased throttle. So the driver eases off the accelerator and the transmission upshifts to the higher gear, sensing less engine load. The car begins slowing again, whereupon the driver presses on the throttle, and the transmission once again downshifts. This cycle of accelerating and decelerating, downshifting and upshifting, is called "gear hunting" and will repeat until the top of the hill is reached or the driver manually downshifts.

Likewise, when driving on downgrades without Grade Logic, the transmission senses a closed throttle with high vehicle speed and upshifts to 4th or 5th gear, rather than downshifting to permit engine braking. To slow the vehicle, the driver may have to step on the brake pedal, or manually downshift to a lower gear to slow it down.

Grade Logic eliminates these problems because it uses throttle position, brake-pedal position, road speed and rate of deceleration and acceleration to determine actual driving conditions. It then uses this information to select the appropriate program from its stored computer shift maps. For example, when driving uphill, Grade Logic senses that despite a large throttle opening, the car is not accelerating and picks the uphill driving shift map that holds in gear and delays upshifts, thereby eliminating hunting between gears.

When driving downhill, Grade Logic senses that the vehicle is going downhill. It then selects the downhill-driving shift map and selects and holds a lower gear to also provide engine braking. Similarly, if it senses bursts of acceleration and deceleration, actions that typically accompany driving on a winding road or in stop-and-go traffic, it chooses a shift map that holds the transmission in gear and delays upshifts, making rapid acceleration possible."