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Rough Idle

Tiny
TOPCAT1961
  • MEMBER
  • 2005 FORD TAURUS
  • 6 CYL
  • 2WD
  • AUTOMATIC
I have a 2005 Taurus SEL with 123K miles. The engine runs a little rough at idle and the tach jumps up and down about 50 RPM when the car is sitting still. It runs fine on the hiway and MPG is 29-30. I replaced plugs, had a smoke test run for vac leaks, (fixed one on PCV line), but no other leaks were found. I cleaned the throttle body and MAF sensor also and replaced the air filter. Does anyone have any other ideas? I have been told that a broken tooth on the cam syncronizer can cause this but it is not making any chirping noise.
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Monday, March 14th, 2011 AT 7:44 PM

15 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Go to this link: https://www.2carpros.com/articles/engine-misfires-or-runs-rough
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Monday, March 14th, 2011 AT 8:52 PM
Tiny
TOPCAT1961
  • MEMBER
  • 5 POSTS
  • 2005 FORD TAURUS
  • 6 CYL
  • 2WD
  • AUTOMATIC
My Ford Taurus is running a little rough. I have had the car checked for vac leaks with a smoke mach and given it several gas treatments. Replaced plugs 6 months ago, all gapped properly. The computer is showing 29.6 mpg (I take some long hiway trips). Also, why does the AC compressor cycle on every 14 sec or so even if I am using the heater? I can feel the car surge and the RPMs jump when this happens and it is driving me crazy. On vent setting (11 o'clock position on air select dial) this does not happen, on all other settings it does. Car has 123K on it. Thanks.
Topcat1961
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Check A/c system as its sounds as low on refrigerant

The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
The panel/floor door, defrost door vacuum control motors are at no vacuum, directing airflow to the defroster duct and the side window demisters.
The temperature can be adjusted to heat or cool the air below the outside temperature.
The A/C compressor will operate if the outside temperature is above approximately 6°C (43°F).
The blower motor is on.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
TOPCAT1961
  • MEMBER
  • 5 POSTS
Ok, BMRFIXIT, this is all very intresting but, if I am understaning your reply properly, the answer is : Yes, the AC compressor will cycle on and off in every setting on the dial except the air inlet setting which is located at the 11 o'clock position on the dial.
Is this correct or not? Also, I would like to know someones thoughts on the rough idle part of the question as well.
Topcat1961
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
My understanding its happening only when AC compressor on

and if so 1st should have the AC charged and Check for leaks
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
ANTHONYB61
  • MEMBER
  • 1 POST
  • 2005 FORD TAURUS
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 66,000 MILES
My car idles rough mostly when cold. Also when braking and coming to a stop, car will hesitate and feel like it is going to stall. This will continue when stopped and as I am accelerating from stop. When on the highway, it seems to run fine. I have replaced the mas airflow sensor. When checking codes I get P0174 and P0171. I understand these codes to indicate a number of different things, like vacuum or oxygen sensors. But these codes indicate oxygen sensors on different banks. I'm not finding any obvious vacuum leaks. I also change the fuel filter. Please help, I'm going around in circles.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
Its an indication of a vacuum leak
best to have it smoke tested
if can not find the leak visually
most common to find intake manifold and gasket
check PCV valve hose too
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
MED1562
  • MEMBER
  • 5 POSTS
  • 2005 FORD TAURUS
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 115,000 MILES
Had transmission rebuilt less than 2 months ago. Now I have been having periods of intermittent rough idling and hesitation when pressing gas pedal either from a start or when getting on the freeway. I have changed the spark plugs, wires and fuel filter.
Code that comes up when checked is P0353 Ignition Coil C Primary/Secondary circuit malfunction.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Have you checked wiring to the coil to make sure everything is tight, clean and undamaged?
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
MED1562
  • MEMBER
  • 5 POSTS
All wiring to the coil looks to be in good shape and tight at connections.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
If that is all good, I would think the coil is bad. You may want to remove it and have it checked.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
MED1562
  • MEMBER
  • 5 POSTS
Primary and secondary coil ohn test showed the coil to be good.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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There must be a wiring issue. Check to make sure wires are not damaged.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
MED1562
  • MEMBER
  • 5 POSTS
After checking all the wiring and connectors for anything that looked like it could be bad I decided to change the ignition coil and have not had any problems since changing it four days ago.
Thanks for the great advice.
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Great! Let me know if you have questions in the future.

Joe
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Wednesday, April 3rd, 2019 AT 1:52 PM (Merged)

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