Chasing a rougher idle after spark plug change

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Changed out the plugs on my Forester last month or so, used the factory type NGK FR5AP-11. Service manual says gap to be between 0.39 - 0.43, they showed 0.44 out of the box so I set them to 0.41. After several weeks of the idle dropping almost to stall upon downshift clutch engagement (manual trans) and actually worse fuel economy than before, I finally had the epiphany to perform the idle re-learn procedure recommended on some subaru forums, since I had removed the battery to get to the driver side plugs. Well, I can tell you that the procedure is for real because it solved the momentary idle dropouts on down shift and fuel economy returned to normal. But, the idle is still lumpier than before. Before, there was very little if any shake, now there persists some shake that wasn't there and I can hear a random miss at the exhaust tips that clears up once some rpm's are added. Does this sound like ignition wires? I had to tug like [censored] to get the boots off the plugs, they hadn't been touched since the factory put them on in 2008. They're those deep reach type about 6" long and stretched a lot as I pulled them off. The wires are Packard which is usually carbon core. I'm wondering if the boots stretching during removal upset the conductive material enough to cause the random idle chuggle. Probably replace the wires, yes? Coil (waste spark type) is fairly new only about 7000 miles (failed and threw misfire codes, replaced no charge by Subaru under a TSB).
 
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Carbon core wire ought to be replaced with some good NGK wire wound suppressor stuff. That was a save a buck move by the factory.
 

LoneRanger

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Doesn't seem possible. To prevent cross threading or other damage, I used a length of 3/8" rubber fuel line pushed onto each plug to spin them down to gasket contact then put the socket on to torque to spec. That works really well by the way and its impossible to cross thread since the hose is too weak to cause any galling.
 
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Looks like a clogged, a bad injector coil or sticking injector to me. My Impreza got that, and a little TCW3 oil got rid of that real quick. Thanks BITOG!
 
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Tune in a weak AM radio station with the engine on. If you hear ignition noise, checking the wire and coil connections is a good idea. Sometimes a portable AM radio moved around the engine compartment can give a clue. (This comes from years of running HF radio gear in cars) Poke the wires a little with with a stick, don't grab them. smile
 
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Originally Posted By: LoneRanger
What's TCW oil, do you put it in the gas and does it hurt O2 sensors?
It's used to "lube" the injectors. Synthetic TWC (Two cycle watercraft) burns very cleanly. I don't use it, I use one of the few Lucas products which seems worthwhile, their fuel system cleaner, ( sold at Wallyworld) But I only use the stuff in my twin carb BMW bike and carbed power equipment where it seems to help with things like tank rust and, especially, sticking carb floats. The lubrication quality avoids what we call "Bingfoot" which is a fuel soaked boot because of leaking float chambers caused by sticking floats on a flat twim BMW bike motor. THere's a little overflow vent on the bowl from which the excess gas drips, right on to your boot. (Bing carbs) I suspect TWC might do the same thing in a small dose. I'm not the biggest "German Engineering" fan on BITOG, I love the old boxer bike but German Engineering .... Ahhhhh OOOOF sometimes.
 
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Originally Posted By: redbone3
Occam's razor suggests the ignition wires.
I agree too. Likely damaged the core with all that pulling.
 
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Originally Posted By: LoneRanger
Does this sound like ignition wires? I had to tug like [censored] to get the boots off the plugs, they hadn't been touched since the factory put them on in 2008.
Were you tugging on the boots or the wires themselves? On my Buick, GM used an adhesive between the boots and the plugs. I got the boots off, but nose pliers destroyed the boots.
 

LoneRanger

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The boots. They have a butterfly type grip thing molded in at the top of the boot where you're supposed to get your fingers under and pull. Grasping with my right I had to wrap my left around my right hand to maintain grip on account of how much force I had to pull with. Streeeetchs like the old 70's action figure Stretch Armstrong and finally comes off, then BAM into the side of the engine compartment slams the back of my hand (horizontal boxer engine cyl heads + tight clearances). Lather, rinse, repeat x 4.
 
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Are you sure you didn't bump into something when you were in there? These engine compartments are so tight these days, it's easy to knock something off and not even know it. I remember getting an EGR code when I changed mine. After about 10 minutes of panicking, I finally found the little EGR vacuum hose that I knocked off.
 
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Originally Posted By: HerrStig
Originally Posted By: LoneRanger
What's TCW oil, do you put it in the gas and does it hurt O2 sensors?
It's used to "lube" the injectors. Synthetic TWC (Two cycle watercraft) burns very cleanly. I don't use it, I use one of the few Lucas products which seems worthwhile, their fuel system cleaner, ( sold at Wallyworld) But I only use the stuff in my twin carb BMW bike and carbed power equipment where it seems to help with things like tank rust and, especially, sticking carb floats. The lubrication quality avoids what we call "Bingfoot" which is a fuel soaked boot because of leaking float chambers caused by sticking floats on a flat twim BMW bike motor. THere's a little overflow vent on the bowl from which the excess gas drips, right on to your boot. (Bing carbs) I suspect TWC might do the same thing in a small dose. I'm not the biggest "German Engineering" fan on BITOG, I love the old boxer bike but German Engineering .... Ahhhhh OOOOF sometimes.
^^^This. I had this problem a bunch of times, and MMO (best result) or TCW3 oil (very good results and inexpensive), made that misfire at idle good by! I use 1 part of TCW3 oil for 500 parts of gasoline (Shell V Power premium not needed anymore, thans Bitog!! Doesn't hurt anybody's O2 sensor. There's hundreds of members here that use it and much more elswhere.
 
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