High idle problem-Help!!!


sluhbmet

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About a month ago I decided to perform a much needed tune-up on my stock 95 4.0 Ranger ext. cab 4X4 5-speed, because the idle seemed to fluctuate a little (between 500-750 rpm). I started with new Autolite spark plugs. I inspected the plug wires, and all connections appeared clean and shiny, so I did not replace them. I replaced the fuel and air filter next. I purchased the correct cleaners for the MAF sensor and the throttle body assembly. I cleaned both the throttle blody and MAF sensor assemblies to pristine condition. I allowed them to dry and then reinstalled them. The next step was the idle air controller. I removed the idle air controller and found some carbon buildup inside it. I used carburetor cleaner to clean out all of the buildup and let it dry before installing back on the truck. Ever since then, the truck starts perfectly but when I come to a stop light and push in on the clutch, the idle stays at about 1500 rpm for several seconds, then gradually steps down to about 900 rpm's. I did some research and found that I may have damaged the throttle position sensor while spraying the throttle body with cleaner. I replaced the throttle position sensor with a new motorcraft/ford one from the parts store. Replacing it did not help the problem, so I figured maybe I damaged the IAC when cleaning it. Replaced the IAC with a Borg-Warner replacement from the parts store. This also did not help. I am now at almost a total loss as to what the problem could be. The only two things I can think of would be maybe the intake air temp sensor was damaged during cleaning or maybe I bumped a vacuum hose loose when replacing the spark plugs. There are no "check engine" lights on, and I did not touch the idle set scew when cleaning the throttle body assembly. Also, I unhooked the battery from the truck for about 4 hours to reset any bogus values stored to the ecm during parts swaps, this also did not help. Any help from you guys would be greatly appreciated. Thanks in advance for your replies.

Sluhbmet
 


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almostclueless

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A lot of folks think the cleaning the IAC is a temporary fix.
 

Ranger5.0

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unhooking the batt to "reset codes" isnt realy a good idea tho, the ecm "learns" how your engine operates and saves this data as a referince. Also, throwing parts at it because of a hunch, or somthing somone said isnt good either, it gets costly fast. Try looking for an vacume leak, you might be able to hear it as it will sound like a high pitched hiss i guess is the best way to put it. Also, some problems with a ecm imput will not flag a trouble code OR will flag a code but not set the cel. Erratic idle can becaused by a vac' leak...start there and see what you find.
 

sluhbmet

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Thanks for the tip on the vacuum leak. I'll try to dig up some information on how to test the vacuum system and see what results I get.

Thanks again,
Sluhbmet
 

Ranger5.0

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cheep and dirty vacuum leak test: Fire up the engine, put it in park, or neutral with the e break on "for safty" dont want ya gettin run over by your own truck right ? K, you can either use an un lit i say again UN LIT propane torch, open the valve DO NOT LIGHT IT UP and poke it around your vaccume lines, around your throttle body, down around your intake manafold gasket. If the idle changes while doing this, note the location in the engin compartment, and start taking a closer look. you can also use a can of parts clean and spray it around the engin compartment and check for a change in engine speed. If you use parts clean, keep in mind that its highly flamable, like, will burst into flames it you look at it the wrong way on a hot day. So keep it off hot engine components.
 

94redranger

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does a cracked head or bad head gasket possibly cause this high idle? I know my head or head gasket is bad and I have the same problem when I puch the clutch in it revs up to 1500 and stays there for several seconds
 

Ranger5.0

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well, when things arnt properly sealed then anything could happen...its hard to juss give an answer without some details.
 

Aubrey

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I have exactly the same problem and symptom with my 91! Rev's fast but gradually steps down at a stop light. I had the heads off last year and was thinking I might have an intake manifold leak. But lately I've been wondering if the MAF sensor is worn out. I cleaned mine like you did. But it's an expensive part to replace on a guess. Is there a tried and true way to test the MAF?
 

Aubrey

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cheep and dirty vacuum leak test: ...you can either use an un lit i say again UN LIT propane torch, open the valve DO NOT LIGHT IT UP and poke it around your vaccume lines, around your throttle body, down around your intake manafold gasket. .
That's a great idea! A little propane sucked into the right place (like a leak) will rev it up!
 


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