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Slight rough idle after spark plug change

mikepier

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A couple of months ago I replaced the spark plugs on my 99 XLT SOHC. Rather than go with the Motorcraft, I went with the Autolite plugs. I can't recall which ones I used, the platinum AP103, or the double platinum APP103, but in any event, I also replaced the wires with a generic brand called Standard.
The truck starts and runs fine except for one thing I noticed. While at a light I notice a slight roughness or vibration in the truck. If I put the truck in neutral its fine. I figured it something to do with the plugs , but I gapped them correctly. Anyone have issues with the Autolites? Could using the wrong plug affect the idle?
 



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team

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i would make sure all the wires are on tight first. I haven't had any probs. with autolite myself, and i am currently using them. If you want to you could check the resistance of your wires, shouldn't be more than 7,000 ohms per foot.
 






96eb96

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A couple of months ago I replaced the spark plugs on my 99 XLT SOHC. Rather than go with the Motorcraft, I went with the Autolite plugs. I can't recall which ones I used, the platinum AP103, or the double platinum APP103, but in any event, I also replaced the wires with a generic brand called Standard.
The truck starts and runs fine except for one thing I noticed. While at a light I notice a slight roughness or vibration in the truck. If I put the truck in neutral its fine. I figured it something to do with the plugs , but I gapped them correctly. Anyone have issues with the Autolites? Could using the wrong plug affect the idle?

How did you route the wires? Same positions as the old ones? Did you use dielectric tune up grease in the boots? The standard brand wires may not have grease.
Plugs gapped to spec? Plat plugs have to be gapped using the ground electrode, if you push on the tip it could break.


I would worry more about the wires. Fords seem to work very well with motorcraft plugs and wires.
 






Four0Sport

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autolite manufactures motorcrafts plugs so you did right by buying the autolites. i would bet your problem lies in the cheap wires, you get what you pay for. i have had very good luck with autolite wires.
 






mikepier

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autolite manufactures motorcrafts plugs so you did right by buying the autolites. i would bet your problem lies in the cheap wires, you get what you pay for. i have had very good luck with autolite wires.
Thanks for the responses.
One thing I noticed about the Standard wires is on the end that plugs into the coil, the metal conductor that sticks out of the boot was a bit shorter than on the Motorcraft wires. I don't know if that would make a difference since the truck runs great otherwise, but I'll keep it in mind.
 






Four0Sport

Jack Pewe
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even with some of the autolite wires ive purchased.. mass production will sometimes lead to small errors. sometimes the metal prong that sits in the coil pack is pushed out too far from the plastic lock or too far in. you might want to play with the prongs by gently pulling the plastic lock back on the wire. you know its at a good length when you sit the wire in the coil pack and you have slight resistance while pushing the lock over the rim of the coil pack. make any sense? lol
 






mikepier

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even with some of the autolite wires ive purchased.. mass production will sometimes lead to small errors. sometimes the metal prong that sits in the coil pack is pushed out too far from the plastic lock or too far in. you might want to play with the prongs by gently pulling the plastic lock back on the wire. you know its at a good length when you sit the wire in the coil pack and you have slight resistance while pushing the lock over the rim of the coil pack. make any sense? lol


Otherwise could it be the IAC starting to act up? It is 10 years old, and I don't know how long they last.
 






Four0Sport

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if the problem first occured after the tune up i would double check that first. the IAC will give you a loud wine usually when it goes out. although taking it off and cleaning it out doesnt hurt. theres as good thread on cleaning the IAC if you search for it.
 






mikepier

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if the problem first occured after the tune up i would double check that first. the IAC will give you a loud wine usually when it goes out. although taking it off and cleaning it out doesnt hurt. theres as good thread on cleaning the IAC if you search for it.


Just out of curiousity, what is the engine RPM's suppose to be in gear at a light? My tach says about 600. If I step on the gas a little to get it at 750, the truck idles better.
 






bluestream1

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My truck idles at 600rpm. FWIW, I have had the same problems for as long as I have had my truck. Just learned to live with it...
 






bluestream1

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Just out of curiousity, what is the engine RPM's suppose to be in gear at a light? My tach says about 600. If I step on the gas a little to get it at 750, the truck idles better.

My truck normally idles at 600 RPM and I get the vibration. Strangely, it will sometimes idle at around 750 and no vibration. No rime or reason to when it does this., and I have given up looking for a solution. About 25% of the time when I stop at a light I get the higher idle with no vibration.
 






mikepier

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My truck normally idles at 600 RPM and I get the vibration. Strangely, it will sometimes idle at around 750 and no vibration. No rime or reason to when it does this., and I have given up looking for a solution. About 25% of the time when I stop at a light I get the higher idle with ni vibration.


Same here. If I lightly step on the gas to get it up to 750, its fine. Sometimes when I let go it will drop to 450-500 and idle fine. 600-650 seems to be the magic number for this vibration, like if the engine and components were tuned to a resonant frequency to vibrate at a certain RPM's
 






eXcali

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I picked up a set of cheap plug wires only to find the rubber melted and I was getting an arc. It really is worth the extra money to get a quality set. If your tight on money, put the original wires back in one at a time to see if you can find any bad wires.
 






Cobraguy

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It is very easy to crack a plug if you don't use the proper socket. (insulated plug socket) And even then, if you are working in a tight area, it can crack. If it is, it can be difficult to see. You might want to have a balance test run and see what cylinder is missing so you can concentrate on that plug, wire, compression, etc.
 






mikepier

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autolite manufactures motorcrafts plugs so you did right by buying the autolites. i would bet your problem lies in the cheap wires, you get what you pay for. i have had very good luck with autolite wires.

Ironically, the Standard Motor Products ignition wires sell for about the same as Autolites Wire Set on Advanced Auto Parts website. So now I'm wondering if its worth buying new wires or perhaps checking maybe the gap or the wires themselves if they are loose.
 






amyrvik

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The IAC

I agree with the forum in that correct high quality plug wires are essential for completing the circuit. Am I correct in understanding that the Motorcraft brand are the best to purchase?

Also, I cannot get a grasp on what the IAC is. A comment was made that it makes a strange noise as it goes to failure mode. I would appreciate it very much to have this part explained to me.

I think I have found the double platinum plugs for my '02 Explorer Sport Trac 4.0L SOHC so will be replacing those tomorrow along with the wires.

I appreciate very much the input from you all and hope to get my truck running super.

Thanks,

Alan
:usa:
 






robertoa1a

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It is a valve that allows some air to by-pass the throttle body. The PCM can open it and close it as needed. Rember the choke on a carb. Well it's not exactly the same but Somewhat.

I wouldn't take it off and pry the valve open with a screw driver or you might brake it and have to drive to auto zone with it broke.LOL
 






96eb96

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I agree with the forum in that correct high quality plug wires are essential for completing the circuit. Am I correct in understanding that the Motorcraft brand are the best to purchase?

Also, I cannot get a grasp on what the IAC is. A comment was made that it makes a strange noise as it goes to failure mode. I would appreciate it very much to have this part explained to me.

I think I have found the double platinum plugs for my '02 Explorer Sport Trac 4.0L SOHC so will be replacing those tomorrow along with the wires.

I appreciate very much the input from you all and hope to get my truck running super.

Thanks,

Alan
:usa:

Motorcraft is the best you can get for Ford products. There may be other good products but you can't go wrong with M/C.

Like Robert said it is a bypass. Think of it as a little man that holds your gas pedal down just a bit so you don't stall. It doesn't physically move the pedal but allows air to enter the intake.
The IAC can fail with or without a noise, generally if you have difficulty idling or staying started it can be going bad.
 






410Fortune

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I want to add gapping platinum plugs is not always a good idea
you can knock the platinum coating right off of the electrode
I have found 1 platinum plug out of about 50 that needed gapping, and this is because dumbass behind parts counter dropped it and I was like its okay they have cardboard protectors... little did I know Autolites dont come with the cardboard doo dad

Clean your MAS sensor and reset your computer, see if your stumble at idle goes away
 



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96eb96

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I want to add gapping platinum plugs is not always a good idea
you can knock the platinum coating right off of the electrode
I have found 1 platinum plug out of about 50 that needed gapping, and this is because dumbass behind parts counter dropped it and I was like its okay they have cardboard protectors... little did I know Autolites dont come with the cardboard doo dad

Clean your MAS sensor and reset your computer, see if your stumble at idle goes away

good advice, never use the inner electrode as leverage when you gap. The platinum is very delicate.
 






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