..... took my foot off the gas pedal to begin slowing down for an exit ahead. The engine revved up probably 750RPM to about 3500. Then it did it again, and then on the off ramp it was somewhere about 1500RPM instead of 750-1100 RPM.
I would suspect a dirty or faulty Idle Air Controller. Clean the IAC. Replace the IAC if the symptoms persist.
Cleaning the Idle Air Controller (IAC) :
Purchase sensor safe Throttle Body cleaner spray.
1. Remove the Throttle body from the intake manifold.
2. Remove the IAC with a TORX 15 driver (2 bolts)
3. Gently wiggle out the IAC from the throttle body
4. Clean the IAC with Throttle Body Cleaner (not carburetor cleaner). Use cleaner, a rag, and a toothbrush. Be gentle; don’t twist or pull on the pintle as it is fragile and can be damaged easily
5. Also clean where the IAC seats in the throttle body with the same throttle body cleaner
6. While you have the Throttle Body off, give it a good cleaning also.
7. Reinstall IAC, the Throttle body, and check idle quality.
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