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Old 03-30-2007
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Join Date: Apr 2006
Location: Harrisonburg, VA
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surging idle problem 96 4.0

My 96 4.0 is having a problem with the idle jumping back and forth between 500-1500 RPM. from searching, ti seems people have had this problem due to everything from MAFs to vaccume leaks. Id like to start by cleaning the IAC. anyone got a picture of where the IAC is in the engine bay? also, the PCV valve while were at it, since ive got a new one.
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Old 03-31-2007
rolsmojave3's Avatar
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Join Date: Jun 2006
Location: Wisconsin
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I have this problem also, I'm going to try a new MAF soon. I tried a new IAC nothing and searched for vacuum leaks but ran out of time. The IAC is located on the driver's side of the throttle body, looks like a short cylinder about 1 inch in diameter. The PCV is located on the driver's side valve cover at the rear (close to the firewall). You will see a short black line running to it from the intake manifold, a flash light will help you on that one.
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Old 03-31-2007
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Join Date: Nov 2006
Location: Connecticut
Posts: 479
Regarding the '97 4.0L and idle problems, another thing to check is the fuel supply manifold (a/k/a/ fuel rail) gasket per the Ford TSB.

Article No. 98-6-8


This TSB article is being republished in its entirety to correct the part number listed, revise the Service Procedure, and add Aerostar.

A rough idle, stalling at an idle and/or Diagnostic Trouble Codes (DTCs) P0171, P0174, P1131, and/or P1151 may be stored in memory on some vehicles with a 4.0L engine. This may be caused by the gasket located between the fuel rail and lower intake manifold losing its compressive loading and becoming drawn into the intake manifold runners resulting in a vacuum leak.

Replace the fuel rail-to-intake manifold paper gasket with a revised gasket. Refer to the following Service Procedure and the 1997 Ranger or Aerostar Service Manual for removal and replacement procedures...

F8PZ-9E436-AA / Fuel Rail-To-Intake Manifold Gasket
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Old 04-02-2007
rolsmojave3's Avatar
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Join Date: Jun 2006
Location: Wisconsin
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Just replaced that gasket today, problem is gone. Take some carb cleaner, and when the truck is idleing like that, spray it below the IAC and back towards the firewall. It's not that hard to replace, there is a "how to" on this site for it, took only 2 hours and that is working slow.
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