When driving my Corolla with the cruise control engaged and I go up (or Down) a relatively small incline the engine speed will quickly increase from about 2,000 rpm to over 4,000 rpm (it sounds like the engine is coming apart). I spoke to the Toyota Service Manager and he said this is normal operating processes and not to disengage the Cruise control because it will go back to normal. My question is; is the normal for all corolla’s? Will the increased RPM harm the engine? Does this need to be corrected? Is there a fix available? Should I just ignore this or just not use Cruise control? Any advice would be appreciated. Thanks
How long have you had this vehicle ? This is normal operation and No , 4000 RPM is not going to harm anything . Just set the cruise and relax , the engine controls will not allow any harm to the engine.
The car downshifted to a lower gear to maintain speed on the hill. Exactly what should happen.
If it doesn’t when you drive manually, I’ll bet you slow down going up the hill! 
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I’ve owned the car about 3 months.
It just seems odd that the RPM would significantly increase when going downhill with the cruise control engaged.
Thanks for your reply!
That is engine braking to keep you from getting a speeding ticket at the bottom of hill .
The RPM shoots up to 4,000 after I’ve crested the hill and I am going downhill!
Thanks for your response.
Might have been useful to know that from the beginning. Anything else you are holding back?
A Corolla’s Cruise Control (as well as all other basic cruise control systems), only use the engine and transmission to regulate speed, they don’t use the brakes. As Volvo_V70 mentioned, it is maintaining speed downhill, by utilizing engine braking. To brake using the engine, the transmission shifts to the appropriate lower gear, which raises your rpms. Even though your engine speed is increasing, if the engine is performing braking, LITTLE TO NO FUEL IS BEING USED.
Your Corolla is working as intended and you have nothing to worry about. If you don’t like loud engine noise, do what I did, buy an EV (2019 Chevy Bolt here).
I put nearly a quarter million miles on my 2006 Corolla in a decade of ownership. I redlined the tach (went up to 6500 rpm, manual trans) with the engine at operating temperature, just about every time I drove it! It was so boringly reliable and I was tired of driving it. Now it sits in my driveway, hoping for gas prices to go up, so the value does as well.