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Why is my car revving up while in neutral?

Tiny
AFTRBURNRS
  • MEMBER
  • 2002 MAZDA TRIBUTE
  • 80,000 MILES
Whenever I take my car out of gear it begins to rev up and can get up to 4000rpms or higher. I just replace the IAC and it has not helped.
Friday, November 18th, 2011 AT 1:54 AM

8 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Have you checked for vacuum leaks? Fuel pressure?
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Friday, November 18th, 2011 AT 3:27 AM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Did you check for trouble codes?
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Friday, November 18th, 2011 AT 1:08 PM
Tiny
AFTRBURNRS
  • MEMBER
  • 4 POSTS
Engine light had been on and showed that I needed to replace my IAC which I did. I am about to clean the throttle, MAF, and change the air filter and PCV valve. How do I check for vacuum leaks?
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Friday, November 18th, 2011 AT 6:08 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Go to our homepage under the DIY section for directions on checking for vacuum leaks. Let me know what you find.
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Saturday, November 19th, 2011 AT 1:32 AM
Tiny
AFTRBURNRS
  • MEMBER
  • 4 POSTS
Engine code is P1506, have not found a vacuum leak yet
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Monday, November 21st, 2011 AT 7:31 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
If the replaced IAC was shorted, there is a possibility the POCM could have been damaged.

Here is a description of the problem and possible causes.

DTC P1506: IDLE AIR CONTROL SYSTEM - MALFUNCTION

Detection Condition

DTC P1506 indicates PCM detected an engine idle speed more than desired RPM. Idle Air Control (IAC) valve controls engine idle speed and provides a dashpot function. IAC valve meters intake air around throttle plate through a bypass within the IAC valve assembly and throttle body. PCM determines desired idle speed or bypass air and signals IAC valve through a specified duty cycle. The IAC valve responds by positioning to control amount of bypass air. PCM monitors engine RPM and increases or decreases IAC duty cycle in order to achieve desired RPM.

Possible causes are:

a) Vacuum leak.

B) Damaged IAC valve.

C) Damaged PCM.

D) Damaged throttle body.

E) IAC circuit short to GND.

F) IAC valve stuck open.
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Tuesday, November 22nd, 2011 AT 11:42 AM
Tiny
AFTRBURNRS
  • MEMBER
  • 4 POSTS
Turns out that my accelerator cable was not allowing my throttle to close completely. Fixed and runnning well now.
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Tuesday, December 6th, 2011 AT 7:43 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Glad you got it fixed.
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Tuesday, December 6th, 2011 AT 7:57 PM

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