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Fluctuating engine idle

Tiny
LWRDR123
  • MEMBER
  • 1999 HONDA CIVIC
  • 1.8L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 263,786 MILES
Car starts up idles good then after a few minutes idle drops down and it almost stalls stays that way for about 1 minute then idles back to normal. It repeats this cycle continuously. Don't know what to do. Help, thank you.
Saturday, October 24th, 2020 AT 2:54 AM

1 Reply

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,640 POSTS
Hi,

The idle speed on this vehicle is controlled by what is called an Idle Air Control valve (IAC). Now, before we assume that is the problem, let's do a couple of checks. First, I would suggest checking to see if there are any vacuum leaks. An engine vacuum leak can cause an idle issue and even a rough idle. Take a look at this link. It explains how to check for a leak.

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

If you find everything is okay, then I would try servicing the IAC. Here is a link that shows how it's done:

https://www.2carpros.com/articles/idle-air-control-valve-service

I attached a pic below showing where the IAC is located on this vehicle. It's on the throttle body.

Let's start with this. Let me know what you find or if you have other questions.

Take care,
Joe

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Saturday, October 24th, 2020 AT 9:44 PM

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