Idle goes up and down

Tiny
RATCHETMAN777
  • MEMBER
  • 2004 MAZDA TRIBUTE
  • 2.0L
  • 4 CYL
  • FWD
  • MANUAL
  • 151,000 MILES
This vehicle use to run really well. Last few months the idle has begun to 'hunt', in other words. It goes up and down - (700 - 1000) in just seconds. My ODB II scanner only shows "CAT" Monitor stat and no fault codes are found. On the road the vehicle runs fine but at a stop light will have the tenancy to stall, sometimes, but not always. What do you think is the problem?
Thanks!
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Saturday, June 17th, 2017 AT 7:39 PM

3 Replies

Tiny
HEYMAN1104
  • EXPERT
A lot of things could cause this and not necessarily throw a code. I would start with taking a good long look around at the vacuum hoses under the hood. Look for cracks or hoses that could easily collapse.

At 151,000 miles, if the fuel filter has not been changed, it might be time to do so. A clogged fuel filter could cause a rough idle and stalling. See this article: https://www.2carpros.com/articles/how-to-change-a-fuel-filter

Could also just be a dirty air filter. Change it if you have not already done so within the last 15,000 miles or so. See this article for more information: https://www.2carpros.com/articles/how-to-replace-a-car-air-filter

A dirty PCV valve could cause some unpredictable behavior like erratic running and stalling. They are usually just a few bucks and pretty easy to change. I do not have an article for this one, but it is often on one of the stickers under the hood. The valve pulls right out on every vehicle I have ever worked on, so it should be s simple job.

Also, bear in mind, with it being summer and the weather being warm, running the A/C will cause the idle to naturally fluctuate, because the A/C compressor clutch is engaging and disengaging, putting extra load on the engine and then taking it back off.
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Saturday, June 17th, 2017 AT 8:06 PM
Tiny
RATCHETMAN777
  • MEMBER
Vacuum hoses have no kinks, cracks, collapsation or leaks. The Air filter and Fuel filter are brand new. PVC valve just changed. Any other ideas?
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Tuesday, June 20th, 2017 AT 2:27 PM
Tiny
HEYMAN1104
  • EXPERT
I should have said to check the Idle Air Control Valve too. Could be dirty or have a loose/bad connector. Or it could just be weak. Try that and let us know.
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Tuesday, June 20th, 2017 AT 2:40 PM

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