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1990 Toyota 4Runner Idle speed is low when the engine is ho

Tiny
CAN_NGUYEN2003
  • MEMBER
  • 1990 TOYOTA 4RUNNER
  • 6 CYL
  • 4WD
  • MANUAL
  • 290,000 MILES
The egine idle speed is about 800 rpm when starting but it will drop to around 500 rpm when the engine is getting hot. Since the rpm is too low when I stop at the stop light, I have to press the gas pedal to keep the engine running. Please tell me what should I check. Also please indicate if possible the photo so it can help me to locate the component I should look for. Thanks.
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Tuesday, July 15th, 2008 AT 3:05 AM

7 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Hi can_nguyen2003,

You need to check the throttle body, most probably it needs a good cleaning.


https://www.2carpros.com/forum/automotive_pictures/192750_210299_Throttle2_1_1.jpg



It is attached to the end of air intake hose on intake manifold.
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Tuesday, July 15th, 2008 AT 12:13 PM
Tiny
CAN_NGUYEN2003
  • MEMBER
  • 4 POSTS
Thanks for your quick response. I follow your advices to clean up the throtlle body, replace air filter but the problem seems not resolved.
After driving for a long trip 10 miles or longer, when stopping the engine to do something like shopping or fill up gas, I restart the engine then the idle speed lower to 500 rpm instead of 800 rpm. Any other suggestiions?
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Wednesday, July 16th, 2008 AT 3:58 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Hi can_nguyen2003,

Is there any changes in idliing speed when AC is turned on or off?

If rpm drops only with AC on, check the AC idle compensator.
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Thursday, July 17th, 2008 AT 8:44 AM
Tiny
CAN_NGUYEN2003
  • MEMBER
  • 4 POSTS
Dear,
The idle speed drops to 500 rpm when hot. If I turn AC on then rpm will increase about 100-150 rpm more.
In the hot day, when travel a long trip the idle speed will drop to 500 rpm when I stop at stop light or restart the engine after refueling.
Thanks,
CN
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Thursday, July 17th, 2008 AT 6:48 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Hi CN,

AC idler compensator is ok.

Is the Check Engine Light showing when driving?

If no CEL showing, check/clean the IAC. Seems the idling air circuit is clogged or sticking at that item.

You might have to separate it from the throttle body to get it cleaned properly. Check valve movement by pushing it. DO NOT use force. One thing to note, there is no service part for the seal so if it gets out of shape, reinstalling might be a problem.

To save all the headaches and time, a replacement would be recommended.
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Friday, July 18th, 2008 AT 12:05 AM
Tiny
CAN_NGUYEN2003
  • MEMBER
  • 4 POSTS
Dear Bob, Ken,
You recommend to replace IAC valve or the Trotlle entirely? I'm not quite sure which part you recommend to replace, Also if you have the photo for IAC valve, please send it.
Thanks,
CN
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Friday, July 18th, 2008 AT 9:33 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Hi CN,

THe IAC comes with the throttle body as a complete unit.

Give the cleaning another try by spraying into the bottom holes in front of the throttle plate. Let it soak for a while and then start engine. With engine started, keep spraying for a while more, open throttle slightly to keep the rpm up slightly. Attach a hose to make the spray reach the inner parts.
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Friday, July 18th, 2008 AT 10:17 AM

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