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How does a faulty temperature sensor cause my car to accelerate without input and redline when stopped?

Tiny
MISSLYSS0829
  • MEMBER
  • 2000 VOLVO S40
  • 11,200 MILES
My Volvos fan was constantly running and outside temp reading seemed high most days, then I started having acceleration issues. My car would take off without me touching the gas. It would even accelerate when I was on the brake. Then I restarted it and the car instantly red lined. Brought it to mechanic twice and they finally figured out it was due to a faulty temp sensor. How does that work? And why would that make my car accelerate? Very scary. Should I replace ETM as well? Please help
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Wednesday, April 4th, 2012 AT 11:17 PM

4 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
Because it's telling the computer that it's 40 degrees below zero outside and the computer richens the fuel mixture and raises the RPMs accordingly although what you are describing sounds too extreme.
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Wednesday, April 4th, 2012 AT 11:59 PM
Tiny
MISSLYSS0829
  • MEMBER
  • 2 POSTS
So this has nothing to do with the throttle?
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Thursday, April 5th, 2012 AT 12:05 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,757 POSTS
Who said that? I just said that the computer will raise the RPMs because it thinks it's real cold outside.
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Thursday, April 5th, 2012 AT 12:08 AM
Tiny
JIS001
  • MECHANIC
  • 3,408 POSTS
Has nothing to do with the throttle. This model does not have the electronic throttle module so there is no "ETM". Still a cable on this. But yes like Wrenchtech says the faulty reading will cause the computer to open up the idle air conbtrol valve to increase the RPMS to try and warm up the engine since it thinks it is very cold.
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Thursday, April 5th, 2012 AT 3:17 AM

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