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A low idle can be a few things. First, I noted that you mentioned the idle air control valve (IAC). Since that is the component that is responsible for maintaining idle speed, that is my first suspect.
With that, let's confirm that it is working. Here is a simple test.
INSPECTION
1. TURN AIR CONDITIONING SWITCH OFF
See Picture 1
2. CHECK IDLE-UP
a. Start engine and run it at idle.
b. Fully turn the steering wheel.
c. Check that the engine speeds decreases when the vacuum hose of the air control valve is pinched.
d. Check that the engine speeds increases when the hose is released.
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If there is no change, remove the IAC and inspect where it mounts for dirt or carbon. Also, here are directions for testing the IAC / power supply:
ON-VEHICLE INSPECTION
IDLE AIR CONTROL (IAC) VALVE
1. INSPECT IAC VALVE OPERATION
a. Initial conditions:
- Engine at normal operating temperature
- Idle speed checked correctly
- Transmission in neutral position
- A/C switch OFF
Pic 2
b. Using SST, connect terminals TC and CG of the DLC3.
SST 09843-18040
c. After engine speed is kept at approx. 1,000 rpm for 5 seconds, check that it returns to the idle speed.
If the engine speed operation is not as specified, check the IAC valve, wiring and ECM.
d. Remove the SST from the DLC3.
SST 09843-18040
2. INSPECT IAC VALVE RESISTANCE
NOTE: "Cold" and "Hot" in the following sentences express the temperature of the coils themselves. "Cold" is from -10 °C (14 °F) to 50 °C (122 °F) and "Hot" is from 50 °C (122 °F) to 100 °C (212°F).
a. Disconnect the IAC valve connector.
Pic 3
Pic 4
b. Using an ohmmeter, measure the resistance between terminal +B and other terminals (RSC, RSO).
If the resistance is not as specified, replace the IAC valve.
c. Reconnect the IAC valve connector.
3. INSPECT AIR ASSIST SYSTEM
a. Initial conditions:
- Engine at normal operating temperature
- Idle speed checked correctly
- Transmission in neutral position
- A/C switch OFF
Pic 5
b. Using SST, connect terminals TC and CG of the DLC1.
SST 09843-18040
c. After the engine speed is kept at 900 - 1,300 rpm for 10 seconds, check that it returns to the idle speed.
d. Stop the engine.
Pic 6
e. Disconnect the air assist hose from the IAC valve, and plug it.
f. Start the engine and check that the idle speed reaches 500 rpm or below (the engine may stall).
If the idle does not reach 500 rpm or below, check for a leak between the air assist hoses, pipe and injectors.
g. Remove the SST from the DLC3.
SST 09843-18040
h. Reconnect the air assist hose to the IAC valve.
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If there are no problems with the IAC, then check to see if there are engine vacuum leaks. Here is a link that shows how that is done.
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
Let me know if any of this helps or if you have other questions.
Take care,
Joe
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Saturday, March 23rd, 2019 AT 10:05 PM