Idles rough when the A/C is not turned on

Welcome to 2CarPros.

When the AC is on, there is a component called a stepper motor that raises the idle speed to compensate for the added load on the engine. When you turn the AC off, the motor (idle air control valve or IAC) readjusts to lower the RPM's.

Based on your description, I have a feeling you have one of three things wrong. First, the IAC is not functioning properly or is dirty, not allowing enough air to enter the engine. Second, there is an engine vacuum leak. Third, the throttle body (throttle plate) needs cleaned.

First, I will provide directions on how to clean a throttle body. This is the easiest to try and cheapest. Follow this link:

https://www.2carpros.com/articles/throttle-actuator-service

Next, if that doesn't fix the problem I need you to check for engine vacuum leaks. This can cause a rough idle as well. Here is a link that shows how to check:

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

Now the last. If there are no leaks and cleaning the throttle body didn't help, I need you to remove the idle air control valve (IAC) for inspection. Again, this is the component that is responsible for maintaining a smooth idle.

First, here is a link that explains how one is replaced. I am providing this just to help you remove the one on the vehicle for inspection.

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

Next, here are the directions specific to your vehicle for IAC replacement. Again, at this point I only want you to remove and inspect it. The attached pictures correlate with the directions. In picture 3, I circled what is called the pintle and have a very sad arrow pointing into where the pintle goes. You need to check for dirt or carbon build up in there as well as on the circled pintle. The very last picture I attached shows where the IAC is located on the throttle body.

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PROCEDURES
IDLE AIR CONTROL (IAC) VALVE REPLACEMENT

REMOVAL PROCEDURE

pic 1

1. Remove the throttle control cable bracket from the throttle body.
2. Remove the canister purge valve.
3. Disconnect the idle air control (IAC) electrical connector.

pic 2

4. Remove the idle air control valve attaching screws.

pic 3

5. Remove the idle air control valve.

pic 4

6. Remove the idle air control valve O-ring.

INSTALLATION PROCEDURE

NOTE: The IAC valve may be damaged if installed with the cone (pintle) extended more than 28 mm (1-1/8 in). Measure the distance that the valve is extended before installing a new valve. The distance from the idle air control valve motor housing to the end of the idle air control valve pintle should be less than 28 mm (1-1/8 in). Manually compress the pintle until the extension is less than 28 mm (1-1/8 in).

pic 5

1. Install the new idle air control O-ring.

pic 6

2. Install the idle air control valve into the throttle body.

NOTE: Refer to Fastener Notice in Service Precautions.

pic 7

3. Reinstall the idle air control valve attaching screws.

Tighten
Tighten the screws to 3.0 N.m (27 lb in).

pic 8

4. Connect the IAC electrical connector.
5. Install the canister purge valve.
6. Install the throttle control cable bracket.
7. The powertrain control module (PCM) will reset the idle air control valve whenever the ignition is turned ON, then OFF. Turn the ignition ON, then OFF.
8. Start the engine and allow the engine to reach operating temperature.

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I hope this helps. Please let me know if you have other questions or just need help.

Take care and let me know what you find.

Joe