Low idle

Tiny
STEPHANIE HEU
  • MEMBER
  • 2002 TOYOTA TACOMA
  • 3.4L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 90,000 MILES
Every time at stops idle drops to 550 rpm. Vibration starts up truck in neutral. All is fine idle fine vibration gone until next stop sign. Checked everything, nothing leaking, no check engine light. Clean throttle body idle air. What next? Shift solenoid not releasing at stop.
Saturday, March 23rd, 2019 AT 8:03 PM

11 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,724 POSTS
Welcome to 2CarPros.

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.

________________________________

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.

______________________________________

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
Tiny
STEPHANIE HEU
  • MEMBER
  • 1 POST
Tried your suggestions, did not solve low idle. Still experiencing low idle in drive gear after warm up during stop at intersection. No vacuum leaks detected.
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-1
Sunday, April 7th, 2019 AT 8:46 AM
Tiny
KMOROI
  • MEMBER
  • 1 POST
  • 2002 TOYOTA TACOMA
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 211,000 MILES
My engine has been hesitating and sputtering when I first accelerate at low rpm. The truck idles fine. This problem started yesterday and getting worse. Check engine light just came on today. About a year ago truck was losing tons of oil so I used Lucas stop leak when I changed my oil and it stopped the leaking. Drove my truck from LA to Ohio two months ago towing pretty heavy trailer. Changed oil before I left and just changed it two days ago. Noticed the smell of burning oil about a week ago after engine stopped. What do I need to have checked? Are my gaskets blown? I used another treatment of Lucas stop leak when I recently changed my oil even though it was not leaking. I used almost 5 quarts of oil plus stop leak quart and now my oil dipstick only shows about half full. Do I need to take it to a dealership or can mechanic fix this?
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
As far as oil leak towing a trailer that far with an oil leak and your oil is down isn't to bad but you shold find the leak and fix it. Otherwise scan for codes and check fuel pressure with a gauge for the other problem. Auto parts rent it and can scan for codes.
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
CARL LABAYAN
  • MEMBER
  • 16 POSTS
  • 2002 TOYOTA TACOMA
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 160,000 MILES
Truck starts then dies. Will not idles unless gas is pressed. A week before the idle would go up and down while parked, from 600 to 1000. Now It will not stay running unless my foot is on the gas. Any ideas? Help!
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Try cleaning the throttle plate on both sides and iac hole with choke cleaner clean shaft area on sides well. They get gummy and do that
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
RYAN L
  • ADMIN
  • 256 POSTS
Check out this video on how to clean the throttle plate! https://www.youtube.com/watch?v=JZoEb_hyWC8
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
CARL LABAYAN
  • MEMBER
  • 16 POSTS
IAC had build up like a battery post. Cleaned IAC Throttle body plates. Changed gaskets. Runs great again. Just wondering how the build up like that of the battery posts got into the IAC. Thanks again
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,536 POSTS
This is normal and it happens to most cars depending on the quality of air the car is run in.

Glad we can help, please consider a small donation to help us keep the site going, the link is below.

Best, Ken
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
CARL LABAYAN
  • MEMBER
  • 16 POSTS
The truck runs okay but at idle after warming up it goes from 750 to 1300 rpms. Cleaned IAC and throttle body. Any ideas? Shoud I clean it again or check for any vacuum leaks? Any help
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
If check engine light is on scan for codes otherwise check for vacuum and air leaks. Air leaks like holes in duct work, grommets bad and leaking etc. Vacuum hoses cracked or broken
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Sunday, April 7th, 2019 AT 8:47 AM (Merged)

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