Idle miss, after overhaul

[tvsubaru]

Background info:

 

So i recently did a head gasket job on my 08 Subaru legacy with the ej253. I've had a oil seep from the passenger side for a while and finally had the time to fix it. Heads were disassembled and sent off to the machine shop to be resurfaced. I cleaned the valves and lapped them back in when i got the heads back from the machine shop. While doing the job I replaced the plugs with NGK iridiums (PN: 5464), and NGK wires (PN: 55004), new Subaru PCV valve, and new air filter. I cleaned the throttle body and MAF as well. The timing belt and water pump were changed at 100,000 miles, so they were left alone. And timing is dead on 100%.

 

I have since put 700 or so miles on the car and have noticed a slight miss at idle on occasion. It usually occurs after starting the car up after it sits and comes to a stop in drive. I unhooked the battery and did a relearn and it seems slightly better, but it is still there. Usually it is more of a idling extremely low, low enough that you can feel each cylinder firing, rather that a cylinder not firing at all. Strange. I've have double checked that the wires are seated securely on the plugs and coils. I read nothing bad about these plugs on the outback forum. What could really cause this? The car has plenty of power and drives excellent otherwise. Additionally I have already tried the old plugs ( it ran worse on the old NGK platinums that were in it). The only think that I question is my valve adjustment, and the wires. The car doesn't tick or anything so i would assume that it is correct. What else could cause this.? http://legacygt.com/forums/images/smilies/spin.gifhttp://legacygt.com/forums/images/smilies/cool.gifhttp://legacygt.com/forums/images/smilies/spin.gif

[Max Capacity]

My first thought was who adjusted the valves ?

 

That may be your problem.

[tvsubaru]

I adjusted the valves and did all of the work myself. I adjusted the valves off of the car ( its a real viable option). But it has made me wonder myself, so I have ordered up 0.008", and 0.010" 12" feeler gauges to make checking it in the car a little easier (Per Max Capacity's suggestion). I will re-check the valve clearance on the car when those come in. If that doesn't fix things, I will probably replace the good looking NGK magnacore wires to see if it makes a difference. Next I'll try replacing the coil if nothing else. My question is this, if the valves being out of adjustment is the cause of my idle miss/vibration, how come the car has no other performance/power issues? I will add that the RPM stays constant, the needle never varies, the MIL is off with no codes, and it feels like a shake at idle. Additionally when I was inside the engine, the cylinders still have the factory crosshatch on the walls; and the car has had full synthetic basically it's whole life, so the heads and valves were as clean as a whistle. The car doesn't use or loose a drop of oil. I do have a Vag-Com cable on it's way to use freessm to see if i can find anything there. Any other thoughts or suggestions would be greatly appreciated. And thank you Max Capacity for you're input.

[rhino6303]

I would try ngk 6371 spark plugs rather than 5464. Your plugs are incorrectly gapped at 0.044". The spark plug should be gapped at 0.039".

 

NGK 6371 plugs are pre-gapped at 0.039".

 

While it may not sound like a big deal an incorrectly gapped plug can lead to misfires and rough idle.

[StkmltS]

sub'd for the love of misfires

[tvsubaru]

Looking through my FSM it says that the plug gap should be "1.0-1.1 mm (0.039-0.043 in).

So wouldn't I want a plug at 0.041 in because that is right in the middle of the range? I did try my old NGK 5463 plugs that were in the car before the work and ran great on; with those plugs in, I think that the car actually ran worse. Why would ngk recommend these plugs if they are at a gap of 0.044" if they are outside the manufacture's gap range? Additionally Au** Zone list the gap at 0.044" as well, Why? I'm going to check the gap on the plugs, and get out my multimeter to check the resistance on the coil and wires and then I will report back. Thanks for you're input everyone.

[StkmltS]

Where are you in Ohio?

If you're close to Cincinnati I've heard that Turn In Concepts is a good place to go.

[tvsubaru]

I actually live outside of Columbus myself. So, I gaped the plugs to 0.041" and checked the resistance on a few things. Between (A) and (B) on the coil I got a reading of 12.38 k ohms, and 12.36 k ohms between © and (D) on the coil. The FSM says it says I should find a reading of 11.2 k ohms +/- 1.68 k ohms (in other words the coil is in spec, but on the higher side of resistance). I also adjusted the clip on one of the wires on the end that attaches to the coil to make it fit more snugly. I thing I may have saw some evidence of carbon tracking in the coil well for cylinder 2 or 4 i believe. That could have also been from the old wires though. I will add that the wires have dielectric grease on each end.

 

FSM spec for wires: My NGK wire's spec:

#1 cord: 7.1 — 12.1 k ohms #1 cord: 265.5 ohms

#2 cord: 12.1 — 19.9 k ohms #2 cord: 0.448 k ohms

#3 cord: 7.7 — 13.0 k ohms #3 cord: 283.6 ohms

#4 cord: 12.3 — 20.2 k ohms #4 cord: 0.454 k ohms

 

My conclusion is the wires are not a problem based upon these readings. I will see how the car drives when I go into work this afternoon, and report back.

I will still adjust the valves again when my new feeler gauges show up.

 

By the way NGK's website says that it is okay to gap these plugs, and I was incredibly careful. These plugs are $7 a piece, and i didn't want to replace them simply on a recomendation.

[tvsubaru]

Didn't notice it last night. However, I Definately felt it shacking this morning on my way to work. As soon as the engine got up to operating temperature it went away almost completely.

[tvsubaru]

The new feeler gauges showed up the other day. The valves were readjusted in car (which is a pain without unbolting the exhaust and engine mounts, and just jacking up the engine) still doable none the less. I had one or two exhaust valves that seemed a little tight, and some loose valves as well. Tight the valves may have been, they weren't tight enough to really have caused any compression loss. The next size down feeler gauge fit them. Also I noticed that when I re-gapped the spark plugs I left those ccv hoses on the valve cover unhooked from the air intake. The car does idle a bit smoother, and feels more like the typical subaru idle.

[StkmltS]

Glad to hear your idle is a little better.

[tvsubaru]

So I'm still dealing with this problem in the car. I now have 7 or 8 thousand miles on the car since I did all of the work to it. The car is still shaking at idle when I get to the first or second traffic light on my way out of town. I did a compression test a few months ago and was reading 175-180 on all of the cylinders. And when I was looking at some data on my laptop I saw that the roughness monitor was counting on Cylinder 1 and 3, but not enough to trigger a light. Thinking that the issue might be a detonation issue I tried some colder plugs on that bank and didn't notice any difference. The car does seam to run a little better on premium though. The idle roughness seems less severe. The car has a new ignition coil (subaru). I just got back from a trip to Boston (about 2,000 miles). The car didn't give me any issues other that the slight roughness after startup. Also I got my highest ever gas mileage on the trip 28.6 mpg. I'm just at a loss as of what is causing this. The car runs great otherwise.

[Max Capacity]

You had me worried there when you talked about premium . I see you have a 2.5i

 

Check the wires to the spark plugs and coil (s) make sure there are not broken.

[tvsubaru]

Yea they are fully seated and not broken. I have resistance measurements on these NGK wires above.