1999 FORD TAURUS ROUGH IDLE

  • Tiny
  • 99tauri
  • 1999 Ford Taurus

Engine Performance problem
1999 Ford Taurus Front Wheel Drive Automatic

my 99 taurus, 3.0L, entech DOHC, developed a rough idle, service engine light is on.

Low mileage (88,900), very clean, nothing obvious wrong.

Any diagnostic suggestions appreciated.

UPDATE:
Had the controller scanned and have 2 codes;
P0171 System too lean (Bank 1)
P0174 System too lean (Bank 2)

Air leak? Gasket? Vacuum leak? Dirty throttle body?

Ideas on where to go from here much appreciated!

Tuesday, March 4th, 2008 AT 6:56 PM

10 Answers

  • Tiny
  • Service Writer
  • Expert
  • 9,254 posts

Start at the beginning and find the codes in the pcm and we can go from there.

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Tuesday, March 4th, 2008 AT 7:49 PM
  • Tiny
  • lglewis7535
  • Member

I have a 1999 Ford Taurus that is having the same problem. Did you ever get an answer as to why this is happening and how to fix it?
Thanks.
Mike

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Sunday, August 10th, 2008 AT 3:54 PM
  • Tiny
  • lglewis7535
  • Member

We have replaced the Gas filter, cleaned out the throttle body and put a new air flow sensor and it still won't idle. Any suggestions!

Thanks.
Mike

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Sunday, August 10th, 2008 AT 4:08 PM
  • Tiny
  • Ford problems
  • Member

What did you determine was the problem with your 1999 Taurus. Mine had the same problems and I did about the same repairs and no improvement

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Thursday, January 1st, 2009 AT 8:01 PM
  • Tiny
  • Dave H
  • Expert
  • 13,547 posts

IDLE SPEED
Idle Air Control (IAC) Valve Assembly
IAC valve assembly is used to control idle speed and provide a dashpot function. IAC valve assembly meters inlet air around the throttle plate through a by-pass within the IAC valve assembly and throttle body. The PCM determines desired idle speed or air by-pass and signals the IAC valve assembly through specified duty cycle. The IAC solenoid is built into IAC valve assembly. IAC solenoid responds by positioning the IAC valve to control amount of air by-passed. PCM monitors engine speed and adjusts IAC duty cycle to achieve desired RPM. IAC valve assembly is not adjustable and cannot be cleaned.

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Thursday, January 1st, 2009 AT 8:07 PM
  • Tiny
  • Ford problems
  • Member

I tried the new IAC and $52 later, no difference in performance. Still holds the RPM too high when you take your foot off the accelerator, acting like the cruise is on but then when the brakes are applied, it will idle down at a light and sometimes, not every time, will die at low idle.

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Friday, January 2nd, 2009 AT 8:34 AM
  • Tiny
  • Service Writer
  • Expert
  • 9,254 posts

Your getting unmetered air by the sounds of it. High idle and the two codes. The brake booster uses vacuum when you press it taking away some vacuum.

Check for a vacuum leak such as around the intake manifold and the pcv hose. Being 10 years old, I wouldn't be surprised if the pcv hose was deteriorated, but check any vacuum source going into the engine.

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Wednesday, January 7th, 2009 AT 8:35 PM
  • Tiny
  • ksolo1007
  • Member

Had same problem with my 1988 crown vic low milage 34k It was in fact unmetered air getting in part time thru a vacuum line to a canister(tab/tad) under the ac compressor that came off. Any vacuum leak will cause this heart ache.

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Thursday, March 19th, 2009 AT 8:18 PM
  • Tiny
  • jgarofalo
  • Member

I have to put in my little bit here.
Ford products since 1992 have a special coating in the throttle body to prevent sludge buildup. These throttle bodies should NEVER be cleaned. The coating actually seals the outside diameter of the throttle plate so that intake idle air is metered through a calibrated hole in the throttle plate. Cleaning or backing off the idle stop screw will damage the throttle body, and as far as I know, there is no repair for it other than replacement.

We have replaced the Gas filter, cleaned out the throttle body and put a new air flow sensor and it still won't idle. Any suggestions!

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Monday, March 23rd, 2009 AT 6:55 PM
  • Tiny
  • 13 jerome
  • Member

If the problem started after you changed the spark plugs retieten the the mass air intake the big thing on top( the gasket under it may be damaged.) I had the same problem here 1 year ago. Did every thing you did this is the problem. No one esle is thinking human error I made a mistake. But man enough to say it. Maybe you did to. Or the gasket is bad but this is what is wroung. Some time it helps to retrace your steps. Glad I could help.

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Wednesday, March 25th, 2009 AT 2:44 PM

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