Engine surges when cold?

Tiny
DAVID PINKSTON
  • MEMBER
  • 2001 NISSAN PATHFINDER
  • 3.5L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
While warming, the engine revs and drops every 2 to 3 seconds repetitively, but when warm, the engine idles normally. Just had U tube above header replaced when Ammco performed valve cover replacement. Said only U tube cracked and needed to be replaced. Checked, and there were no vacuum leaks. Actually started problem after another shop replaced struts with Monroe Quickstruts, sway bar linkages, control arms, and rear shocks. This should have nothing to do with vacuum hoses or header work by Ammco).
Sunday, December 11th, 2022 AT 12:51 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,052 POSTS
Hi,

The idle speed is controlled by what is called an idle air control valve (IAC). Based on your description, that is where I would start.

I attached two pics below to help you locate the part. First, confirm the connector is tight, undamaged, and free of corrosion. If that appears good, then we need to remove it and check to see if there is a carbon build-up in the pintel and the intake. Take a look at this link. It explains in general how to service the IAC.

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

Additionally, if you want a better understanding of this component, take a look through this link:

https://www.2carpros.com/articles/how-a-idle-air-control-valve-works

Let me know your thoughts or if you have questions.,

Take care,

Joe

See pics below.
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Sunday, December 11th, 2022 AT 7:18 PM
Tiny
DAVID PINKSTON
  • MEMBER
  • 1 POST
Thank you very much. Advance Auto said there were no codes (except when they changed the oil and forgot to erase that code). I suspect the IAC needs cleaning, as the pathfinder had a bad oil leak, and Aamco did the repair. Intake manifold was removed, so the IAC is most likely the culprit.
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Monday, December 12th, 2022 AT 9:50 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,052 POSTS
Hi,

That is very possible. If you have a chance, let me know how things turn out for you or if you have other questions.

Take care and let me know what I can do to help.

Joe
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Monday, December 12th, 2022 AT 8:09 PM

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