Fast idle in neutral

Tiny
BALBAUGH
  • MEMBER
  • 2000 MAZDA B2500
  • 2.5L
  • 4 CYL
  • 2WD
  • MANUAL
  • 179,000 MILES
What could cause my idling to go up to 3000-4000 rpm's in neutral?
Friday, August 25th, 2017 AT 4:27 PM

2 Replies

Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
I would suspect either a bad idle air control valve or a vacuum leak (specifically the intake manifold gasket) if there is no service engine light. If there is a light, get it scanned and let us know what the code(s) it has. You can get that done at the local auto parts shop.

Guide on how to check for vac leaks: https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Guide on idle air control (IAC) valves: https://www.2carpros.com/articles/how-a-idle-air-control-valve-works

How to replace an IAC valve: https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac
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Friday, August 25th, 2017 AT 6:43 PM
Tiny
HARRY P
  • MECHANIC
  • 2,292 POSTS
And then I found this. It could be caused by a bad connection at the throttle position sensor. Here is the service bulletin released by Mazda.
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Friday, August 25th, 2017 AT 6:53 PM

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