2005 FFV High Idle With AC On - Taurus Car Club of America : Ford Taurus Forum
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post #1 of 18 (permalink) Old 08-01-2019, 01:52 PM Thread Starter
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2005 FFV High Idle With AC On

2005 Vulcan FFV will not return to normal idle speed when AC is on -- 2500+ RPMs and is difficult to stop at traffic lights or stop signs. No Codes! As soon as the AC is switched off, engine returns to a normal smooth idle and I never see the problem at all if the AC is not turned on. I was able to research this problem on the internet and I found a similar problem for a Taurus with a Duratec engine. That fault was caused by low alternator output when the AC was on, but my alternator is outputting a constant 14+ volts, even with the AC on. I have changed the IAC which has had no effect on the problem. I suspect the PCM but I am reluctant to spend that kind of money without confirmation of my diagnosis. I am also reluctant to take it to a dealer for diagnosis because I am afraid of what that bill might come to. Does anybody have any insight into this problem?
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post #2 of 18 (permalink) Old 08-01-2019, 03:02 PM
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PCMs rarely go bad. In your case the IAC valve is suspect. Aftermarket brands really screw up idles especially when loads like AC is turned on. How is your cold idle.
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post #3 of 18 (permalink) Old 08-01-2019, 03:14 PM
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^+1. Motorcraft only iac recommended. If the replacement iac is aftermarket, may try to clean/oil the old Motorcraft iac if you still have it. If not, buy a new MC or grab an MC from a pick-n-pull jy for your year/engine and clean/oil/install. May clean up and attempt to return the aftermarket iac. I have successfully.
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post #4 of 18 (permalink) Old 08-01-2019, 03:52 PM Thread Starter
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The fault only occurs if the AC is on. When AC is off there is no problem -- normal idle speed and idles smoothly. When the AC is on and the idle is high, the problem immediately goes away when the AC is turned off. Cold idle is fine if AC is off.
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post #5 of 18 (permalink) Old 08-01-2019, 04:11 PM
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Was the previous and current IAC valve an aftermarket. Does the idle change with the defroster on also?
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post #6 of 18 (permalink) Old 08-01-2019, 04:35 PM Thread Starter
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The replacement is aftermarket -- not sure about the first one. The problem does occur when defroster is on. Basically, whenever the compressor is on, I have the problem. The only time I don't have the problem is when the AC control is in the vent position or is off.
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post #7 of 18 (permalink) Old 08-01-2019, 04:47 PM
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Your grounds are suspect. There is a braided ground strap between the engine and cowl area in back of passenger side engine bay. Remove ground screw, clean ground terminals and sand body side at ground screw hole. Put a dab of grease over the area after it's back together to prevent further corrosion.
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post #8 of 18 (permalink) Old 08-01-2019, 04:58 PM
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Quote:
Originally Posted by rsteve56 View Post
Your grounds are suspect. There is a braided ground strap between the engine and cowl area in back of passenger side engine bay. Remove ground screw, clean ground terminals and sand body side at ground screw hole. Put a dab of grease over the area after it's back together to prevent further corrosion.
Pic of the poor job ford did for this. Big eyelet is major current to the body, smaller is PCM ground. Bolted over paint and subject to rust. Simple fix, does not effect PCM memory. Little awkward to reach. Fixed an idle speed issue. I consider this a routine maintenance item.


I do this to all my cars, along with replace the OE pressure cap. Just did that on my most recent used Taurus. High fail rate on that. Ford new design is robust.


-chart-
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post #9 of 18 (permalink) Old 08-02-2019, 05:20 PM Thread Starter
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Thanks for the info. I'll work on it when I get a better weather forecast. It looks like I'll have to remove a lot of the cowling in order to get access to the ground location. I sure hope this fixes the problem.
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post #10 of 18 (permalink) Old 08-02-2019, 05:28 PM
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You should be able to reach that ground without removing anything. The tab it bolts to also can be bent to get a better position with a socket.
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