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Whenever the heat is on auto or A/C on and the car is idling the rmp goes constantly up

Tiny
ALMONDAY
  • MEMBER
  • 2000 MERCURY SABLE
  • 190,000 MILES
You can notice the rpm goes up constantly within few seconds and you can feel the car could move if in gear.
Thursday, April 12th, 2012 AT 3:46 PM

8 Replies

Tiny
ALMONDAY
  • MEMBER
  • 5 POSTS
Something else I forgot to add, the IAC (Idle Air Control) valve was replaced and checked for leaks.
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Thursday, April 12th, 2012 AT 3:48 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,709 POSTS
If the IAC is good, check for vacuum leaks. If the check engine light is on, check for trouble codes. Most parts stores will scan it for free.
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Thursday, April 12th, 2012 AT 3:58 PM
Tiny
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Checked for vacuum leaks, it was ok; furthermore, no engine light on and scan does not bring any code. Big puzzle!
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Thursday, April 12th, 2012 AT 4:23 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Do me a favor. Get a vacuum gauge and check vacuum at the intake. Also, make sure it is steady.
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Thursday, April 12th, 2012 AT 4:34 PM
Tiny
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I picked the car up from the mechanic that he took actually out the intake manifold and did the testing; unfortunately, he didn't find anything else that a piece of wire that was left behind by someone, he thought it was it but no cigar.
He suggested to take the car to an A/C place to see if it could be a relay or something like that.
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Thursday, April 12th, 2012 AT 4:49 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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The IAC is what controld the idle. When the AC is turned on, the IAC should increase the RPM's
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Thursday, April 12th, 2012 AT 5:07 PM
Tiny
WRENCHTECH
  • MECHANIC
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I suspect that the problem is the A/C cycling on and off too frequently. It is normal for the idle to kick up when the compressor comes on but if it's low on refrigerant or has a restriction in the system, it will cycle too frequently.
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Thursday, April 12th, 2012 AT 5:08 PM
Tiny
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Ok, I could check the refrigerant but if it's ok, do you have an idea what else I should be looking into? I'm not mechanical incline so I have to take it to places and everyone what several 'Jackson' just to take a look! Thanks.
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Thursday, April 12th, 2012 AT 5:44 PM

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