#2230385 - 02/02/11 10:26 AM
how do u know if u have a bad IAC
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Member
Registered: 08/04/10
Posts: 120
Loc: Windsor, Ontario, Canada
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Hi i posted a couple times about having bad fuel mileage, a loud humming vibration noise in drive sitting idle and c hugging and sputterin while comin to a stop, someone suggested a bad IAC how do u check and see if its defective or not. And does neone know what a COP is that is the other thing a member told me to check
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2003 Grand Marquis Deep Wedgewood Blue with dark charcoal leather interior Rebuilt Trac-lok 3.27 out of a 07 police interceptor,Dual exhaust flowmaster super 44s for mufflers with H pipe with Mercury Marauder exhaust tips by Megs, Marauder Airbox, cvpi zip tube, ADTR ported plenum, 70 mm throttle body, K&N Air filter, Marauder rims, duck tail Marauder spoiler
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#2230405 - 02/02/11 10:46 AM
Re: how do u know if u have a bad IAC
[Re: Mercinterceptor]
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[email protected]
Grand Poobah
Registered: 03/28/06
Posts: 12731
Loc: ATL
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COP is coil on plug..
the IAC or idle air control valve is what sets and manages your idle. Not really anyway to test it that i know of however.
if you get the horn sound through the intake, high idle or low or now idle stalling I would say replace the IAC as they are somewhat common to going out and cheap/easy fix.
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1993 Lincoln Town Car 150k+ - RIP 5/10/2011 1998 Ford Crown Victoria P71 - RIP 12/25/2006 2001 Ford Crown Victoria P71(Count blackula) 297k+ - Ummmmmm 
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#2230415 - 02/02/11 11:05 AM
Re: how do u know if u have a bad IAC
[Re: 98VicP71]
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Member
Registered: 08/04/10
Posts: 120
Loc: Windsor, Ontario, Canada
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thanks alot 98VicP71
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2003 Grand Marquis Deep Wedgewood Blue with dark charcoal leather interior Rebuilt Trac-lok 3.27 out of a 07 police interceptor,Dual exhaust flowmaster super 44s for mufflers with H pipe with Mercury Marauder exhaust tips by Megs, Marauder Airbox, cvpi zip tube, ADTR ported plenum, 70 mm throttle body, K&N Air filter, Marauder rims, duck tail Marauder spoiler
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#2230443 - 02/02/11 11:47 AM
Re: how do u know if u have a bad IAC
[Re: Mercinterceptor]
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Climber
Registered: 07/09/05
Posts: 656
Loc: Central NY
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Try cleaning it first. It's worked great for me (lasted a couple years before I had to clean it again.)
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2004 Crown Vic Sport - In the midnight gray club!
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#2230454 - 02/02/11 12:04 PM
Re: how do u know if u have a bad IAC
[Re: Mercinterceptor]
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Member
Registered: 04/24/07
Posts: 150
Loc: NC
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From past experience:
If the Idle Air Control is bad the engine will start but run rough, apply some throttle and it will smooth out. If the MAF
sensor is bad the engine will start but stall as soon as throttle is applied or the tranny shifted into gear. You didn't say what year you vehicle was, if it does not have spark plug
wires it has individual Coil On Plug. The COPs are located right beneath the fuel rails. Looks like an oversized bottle cap with a couple of short wires and a connector. Visit your local auto parts store, they should be able to use a scanner and pull a code to indicate what the trouble is. If it's a COP it will tell which one. From the front of the car, the 4.6 cylinders are, on
the passanger side, 1,2,3,4, on the drivers side, 5.6.7 and 8 is
closest to the firewall. To replace a COP, undo the connector,
use a socket, nut driver or screwdriver to remove the small screw holding the COP, pull the COP out, you may have to bend it a little to clear the fuel rail but dont worry, the boot only covers a spring which contact the spark plug. The COP does not clip to the plug. Installation is the reverse. Apply a liberal amount of dielectrec grease to the end of the COP and insert it into the plug hole and press down until the screw holes lines up.
Insert and GENTLY tighten the screw a litte more than finger tight. It only engages by a couple of threads. Strip it and you got problems.
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#2230488 - 02/02/11 12:40 PM
Re: how do u know if u have a bad IAC
[Re: FASTERNU]
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[email protected]
Grand Poobah
Registered: 03/28/06
Posts: 12731
Loc: ATL
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From past experience:
If the Idle Air Control is bad the engine will start but run rough, apply some throttle and it will smooth out. If the MAF
sensor is bad the engine will start but stall as soon as throttle is applied or the tranny shifted into gear. You didn't say what year you vehicle was, if it does not have spark plug
wires it has individual Coil On Plug. The COPs are located right beneath the fuel rails. Looks like an oversized bottle cap with a couple of short wires and a connector. Visit your local auto parts store, they should be able to use a scanner and pull a code to indicate what the trouble is. If it's a COP it will tell which one. From the front of the car, the 4.6 cylinders are, on
the passanger side, 1,2,3,4, on the drivers side, 5.6.7 and 8 is
closest to the firewall. To replace a COP, undo the connector,
use a socket, nut driver or screwdriver to remove the small screw holding the COP, pull the COP out, you may have to bend it a little to clear the fuel rail but dont worry, the boot only covers a spring which contact the spark plug. The COP does not clip to the plug. Installation is the reverse. Apply a liberal amount of dielectrec grease to the end of the COP and insert it into the plug hole and press down until the screw holes lines up.
Insert and GENTLY tighten the screw a litte more than finger tight. It only engages by a couple of threads. Strip it and you got problems.
You have your info backwards for the MAF and IAC. if the car runs rough, bad gas mileage then a dirty MAF could cause that. Dirty MAF may cause some idle issue but the idle is controlled by the IAC so most idling issue in and out of gear are caused by the IAC.
_________________________
1993 Lincoln Town Car 150k+ - RIP 5/10/2011 1998 Ford Crown Victoria P71 - RIP 12/25/2006 2001 Ford Crown Victoria P71(Count blackula) 297k+ - Ummmmmm
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#2230522 - 02/02/11 01:13 PM
Re: how do u know if u have a bad IAC
[Re: 98VicP71]
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Over the Hill
Registered: 09/10/09
Posts: 1501
Loc: Minnesota
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When my car's IAC was bad, it would start that hum/buzz sound whenever I shifted into gear first thing in the morning, accompanied by higher than normal idle speed. It would eventually settle down after a bit of driving.
I've heard mixed results on trying to clean the IAC...I personally just replaced it and have not had a problem since. That's what I would suggest, you have all the symptoms.
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2008 Grand Marquis LS, 138K miles
2014 Chrysler 300C, 97K miles (sold)
2005 Grand Marquis LS, 145K miles (sold)
2000 CVPI, 229K miles (sold)
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#2230705 - 02/02/11 05:06 PM
Re: how do u know if u have a bad IAC
[Re: SPM]
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Member
Registered: 08/04/10
Posts: 120
Loc: Windsor, Ontario, Canada
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Thanks everyone for your input thanks for enlightening me on the cops, I just got those and my spark plugs changed recently and it was doing it before hand so I'm go with switchin out the IAC for now, I'll keep everybody posted
_________________________
2003 Grand Marquis Deep Wedgewood Blue with dark charcoal leather interior Rebuilt Trac-lok 3.27 out of a 07 police interceptor,Dual exhaust flowmaster super 44s for mufflers with H pipe with Mercury Marauder exhaust tips by Megs, Marauder Airbox, cvpi zip tube, ADTR ported plenum, 70 mm throttle body, K&N Air filter, Marauder rims, duck tail Marauder spoiler
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#2230736 - 02/02/11 05:29 PM
Re: how do u know if u have a bad IAC
[Re: Mercinterceptor]
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I know nothing
Posting Addict
Registered: 06/05/10
Posts: 19868
Loc: I can see Detroit from here!
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That Sig is way too big, maximum 600x200 pixels. I'd fix it before a moderator removes it.
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-Steve  2006 Audi A6 ~132k miles, stock. 1998 Mercury Grand Marquis LS HPP ~100k miles, slowly acquiring modifications. 1997 Town Car Cartier ~145k miles, Ported Plenum, Gutted Airbox, Contour E-fan Retrofit, Dual exhaust with Magnaflows, cats deleted, MSD Ignition, KYB Gas-A-Justs, P71 front bar, air ride reinstated, Projector retrofit, Caddy 4-note horn retrofit, Wood rim steering wheel retrofit, holistic weight reduction as the parts fall off.. 1996 Mercury Grand Marquis GS 117,485mi. R.I.P. 7/14/12 
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