Engine revs erratically

Welcome to 2CarPros.

My first suspect, based on your description, is the idle air control valve (IAC) is faulty. The IAC is what is responsible for maintaining the idle speed. What I would suggest is to remove it and inspect it for carbon build up on the end that enters the throttle body. If you look at picture 1, I circled the IAC to help you locate it.

At the end of the IAC is a pintle. The car's computer sends a signal to move that based on engine load and idle speed. On cars with fuel injection, the throttle plate closes completely. As a result, the IAC meters the air that is allowed into the engine to maintain idle speed. A common symptom is the vehicle can't find the correct idle speed.

Here is a link that shows in general how one is replaced. Before you replace it, make sure there isn't a carbon issue on the pintle or in the throttle body where it mounts. Also, if you have someone cycle the key on and off, you should see slight movement in the pintle.

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

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Here are the directions specific to your vehicle for replacement. Pictures 2 and 3 correlate with the directions. Also, a scan tool will be needed for relearn of the new IAC. The directions are at the end.

IDLE AIR CONTROL (IAC) VALVE REPLACEMENT
Idle Air / Vacuum Signal Housing

pic 2

REMOVAL
1. Disconnect the negative Battery terminal.
2. Disconnect the electrical and vacuum harness connectors.
3. Remove the idle air control (IAC) valve attaching screws.
4. Remove the IAC valve assembly.
5. Remove the idle air / vacuum signal housing screws.
6. Remove the idle air / vacuum signal housing assembly and discard gasket.

CAUTION: On IAC valves that have been in service, do NOT push or pull on the IAC valve pintle. The force required to move the pintle may damage the threads on the worm drive. Also, do NOT soak IAC valve in any liquid cleaner or solvent, as damage may result.

Inspection
Use carburetor cleaner and a parts cleaning brush to remove carbon deposits. Do NOT use a cleaner that contains methyl ethyl ketone, an extremely strong solvent, and not necessary for this type of deposit.
Clean IAC Valve O-ring Sealing Surface, Pintle Valve Seat And Air Passage.
Shiny spots on the pintle or seat are normal, and do not indicate misalignment or a bent pintle shaft.
If air passage has heavy deposits, remove throttle body for complete cleaning.
Inspect IAC valve O-ring for cuts, cracks or distortion. Replace if damaged.

NOTE: If installing a new IAC valve, be sure to replace with an identical part. IAC valve pintle shape and diameter are designed for the specific application.

Idle Air Control (IAC) Valve

pic 3

Measurement
If Installing a new IAC Valve measure the distance between tip of IAC valve pintle and mounting flange. If greater than 28 mm, use finger pressure to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage to the valve.

INSTALLATION
1. Install the idle air / vacuum signal housing and gasket.
2. Install the idle air / vacuum signal housing screws and torque (starting in the center and moving outward) to 3.4 Nm (30 lb in.)
3. Lubricate the IAC valve O-ring with engine oil and install assembly.
4. Install the attaching screws and torque (starting in the center and moving outward) to 3.0 Nm (27 lb in).
5. Connect the electrical and vacuum harness connectors.
6. Connect the negative battery terminal.
7. Reset the IAC valve pintle position:
Turn the ignition "ON" for five seconds.
Turn the ignition "OFF" for ten seconds.
8. Start the engine and check for proper idle operation.

NOTE: The Electronic Control Module (ECM) will need to relearn the IAC valve pintle position following battery reconnection. This procedure allows the ECM memory to be updated and provides for a stable idle speed.

Idle Learn Procedure
1. Install the Tech 1 "SCAN" tool.
2. Ignition "ON" engine "OFF".
3. Select the "IAC SYSTEM", then "IDLE LEARN" in the "MISC. TEST" mode.
4. Proceed with the idle learn as directed by the Tech 1 "SCAN" tool.

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One other cause that can cause idle issues is an engine vacuum leak. Here is a link that shows how that is checked:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

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Let me know if this helps. If you have questions or need help, let me know.

Take care,
Joe