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Old 03-10-2018, 06:31 PM   #1
sililis
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Question Bucking when accelerating after changing plugs

A few days ago I noticed some very obnoxious bucking when accelerating above 1/4 of the pedal, so I ran to autozone and got a code about cylinder 3 misfire. Changed the spark plugs out yesterday and the bucking was noticeably smoother. I went and did a couple pulls on it to see if the issue was fully resolved but, lo and behold, when reaching around 4k rpm the bucking is there. Not as bad as it was before the plug swap but something is wrong here. Thoughts? By the way no cel is showing up.
At idle there is a very faint roughness to it as well, when picking up the girlfriend from work before I changed the spark plugs it did get very rough, but not since then, which leads me to think a possible bad MAF sensor? Will be buying a new fuel filter to rule out s**t gas just to ease my mind, not sure how to go about this one. Thanks.

EDIT: Boost is no longer going to appropriate range, only going to 7 psi.. which means there is a probable fault in the vacuum lines or bcs I believe, correct me if I am wrong. Are these two problems correlated? I did mess with the blue cylinder shaped apparatus(what is this?) to get at the passenger side spark plugs and noticed the line going to the tmic was loose, so I tightened it up a ways. Car is acting like I never changed the spark plugs I will have to wait until saturday to check anything unfortunately.
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Last edited by sililis; 03-12-2018 at 10:59 AM. Reason: New information
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Old 03-11-2018, 12:34 PM   #2
subaru_gc8
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try changing to coil
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Old 03-11-2018, 02:30 PM   #3
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cheapest possible solution- get some maf cleaner and clean up your MAF sensor. Most cases, its a dirty MAF- and a 5 dollar fix. =)
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Old 03-11-2018, 04:44 PM   #4
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Sounds like maf or coils. More than likely a coil.
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Old 03-11-2018, 10:03 PM   #5
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I previously cleaned the MAF with some cleaner before this all happened but will go ahead and do so again....today it was worse, hoping maybe I didn't push a coil on all the way hehe. Will test each coil when I get a chance to work on them again. Would it be a bad idea to try a pull and trip a cel? Regardless I will baby it until I find out what the issue is. Thanks.
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Old 03-11-2018, 10:56 PM   #6
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verify the gap on the plugs
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Old 03-13-2018, 11:38 AM   #7
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what kind of plugs where they?

coils as everyone already said is good place to look next. move them around and see if the misfire follows.

If this is registering as severe knock then boost control could become disabled and you would run 7psi at max boost.

likewsie if there is a boost control issue causing sudden surges in boost pressure it could feel like a bucking sensation
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Old 03-15-2018, 01:04 AM   #8
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Quote:
Originally Posted by 86Dreams View Post
what kind of plugs where they?

coils as everyone already said is good place to look next. move them around and see if the misfire follows.

If this is registering as severe knock then boost control could become disabled and you would run 7psi at max boost.

likewsie if there is a boost control issue causing sudden surges in boost pressure it could feel like a bucking sensation
Ngk plugs, and there has been no register as a severe knock. Is there a cel for a bad coil or would it still read as a misfire on that cylinder? I will move the cylinder three coil to a different position and see if that resolves anything. In fact I will just test the coil if I can.

I tested the boost once, I was about 3.2 rpm and there were no surges, just the boost never went past 7psi
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Old 03-15-2018, 08:06 AM   #9
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Quote:
Originally Posted by sililis View Post
Ngk plugs, and there has been no register as a severe knock. Is there a cel for a bad coil or would it still read as a misfire on that cylinder? I will move the cylinder three coil to a different position and see if that resolves anything. In fact I will just test the coil if I can.

I tested the boost once, I was about 3.2 rpm and there were no surges, just the boost never went past 7psi
Seems like you may have a missing restrictor pill in your wastegate lines if you arent bosting past 7
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Old 03-15-2018, 10:25 AM   #10
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A few things here:

1. Your car is 15 years old so quite possibly you have a bad igniter. You should plan on replacing these.

2. Plugs - What type plug? Yeah, NGK but what specific p/n? What did you set the gap to?

3. Fuel Filter - This may help but if it's bad gas ( and it certainly could be ), you will still have to burn through all the bad gas. Get yourself some good fuel injection cleaner. I find Gumout works quite well.

4. You said you cleaned the MAF but how did you clean it and what with? Many people do not clean the MAF properly.

5. IACV - When was the last time you cleaned this, if ever?
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Old 03-15-2018, 12:09 PM   #11
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Quote:
Originally Posted by Samurai Jack View Post
A few things here:

1. Your car is 15 years old so quite possibly you have a bad igniter. You should plan on replacing these.

2. Plugs - What type plug? Yeah, NGK but what specific p/n? What did you set the gap to?

3. Fuel Filter - This may help but if it's bad gas ( and it certainly could be ), you will still have to burn through all the bad gas. Get yourself some good fuel injection cleaner. I find Gumout works quite well.

4. You said you cleaned the MAF but how did you clean it and what with? Many people do not clean the MAF properly.

5. IACV - When was the last time you cleaned this, if ever?
I do not remember the part number on the plugs, but I tapped them to .03 according to nasioc members as well as the guy at Napa. I used a ****ty plug gapper and I'm not comfortable with how accurate it is so once I pull all of them out again I will be using feelers.

As for cleaning the maf, I bout maf cleaner and sprayed up into the mat itself and let is dry out for ten minutes, as well as sprayed the wiring harness.

Never messed with the iacv, wouldn't hurt cleaning but would that really help in my situation? The idle is minimally rough but nevertheless I will take your advice and clean it.

I'll start with the coils and test them to see if they are bad or not firstly.
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Old 03-15-2018, 01:41 PM   #12
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You didn't mention anything about any mods to the car, so if you replaced the OEM plugs with a direct replacement, this should be the p/n on the spark plug: BKR6EIX

The IACV gets dirty over time. Well worth the effort to clean it.
You will need a new IACV gasket unless you are very careful but if the gasket is cracked, you will need one anyway.

To clean the IACV, you should use some type of solvent ( I used alcohol ( not the type you drink )) and some Q-tips.

Once done, let it dry for about 10 minutes before you put it back together.

Dirty IACVs are good for rough idle, misfire codes, etc.

Last edited by Samurai Jack; 03-15-2018 at 01:46 PM.
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Old 03-15-2018, 08:41 PM   #13
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Thanks for the responses samurai, I will indeed clean both the MAF once more as well as the IACV while I mess with making sure the gap is correct on each plug.
As far as mods go I have a catless exhaust and uppipe, and a cold air intake.
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Old 03-21-2018, 10:11 PM   #14
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UPDATE: Cleaned both the MAF and IACV. IACV was dirty, probably never cleaned, but did not fix issue. Boost has been going to 15 pounds, I just never realized it until I pushed more than 3/4's of the way down on the accelerator...but still the problem exists. The bucking is more rough, when putting down the throttle it feels like a vibration...very sudden and quick-like bucking....not sure how else to explain it. Tomorrow I will be pulling out the plugs and checking gap. I can't interchange the coil packs because there is no cel being registered anymore so I am thinking it isn't the coils but a improperly gaped plug or loose connection.
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Old 03-22-2018, 01:02 AM   #15
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its a coil going out on you,my car did the same thing for a long time before the cel went off
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Old 03-22-2018, 08:29 AM   #16
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Sounds more and more like a possible faulty plug and/or igniter. Cleaning the IACV didn't hurt at all.

Check igniters for loose connections at both the igniter and the wiring from the igniter connector to the wiring harness.

Check plugs for damage and gaps. I have gotten a bad brand new plug before so while rare, it can happen.

Once you have validated the connections plugs are good, time to start swapping coils around. Keep track of where they were and where you move them to. Start with cyl #1 igniter and swap it around. If no change, put cyl #1 igniter back on cyl #1 and start with cyl #2 igniter, and so on.

Yeah, it's a PITA, but diagnostics can be just that.

... and just to double-check, you did check for vacuum leaks all around the intake manifold, yes?
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Old 03-22-2018, 11:58 AM   #17
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Hey samurai...I'm testing each coil con action and gap on the plugs right now. Part number is BKR6EGP.... not what you posted about the correct spark plug. My dumb a** didn't cross check t he part numbers with the old plugs(I know, stupid me). Should I go back to the parts store and ask for that exact spark plug and see what's up after I change them? I feel silly now

I settled down after I looked it up, the part number you posted are the iridium versions of what I have, so they are the correct fit. Doh!

I wanted to rule out loose connections before I start swapping coils back and forth, but connections and proper gaping are not the issue. I will start swapping the coils around. But if it is a bad coil, won't the problem still occure even if it is on a different plug?

No loose vacuum hoses or leaks to my knowledge, but will go more in depth on looking when I have the proper set up.

Last edited by sililis; 03-22-2018 at 01:14 PM.
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Old 03-23-2018, 08:25 AM   #18
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Quote:
Originally Posted by sililis View Post
Part number is BKR6EGP....
I settled down after I looked it up, the part number you posted are the iridium versions of what I have, so they are the correct fit. Doh!

But if it is a bad coil, won't the problem still occure even if it is on a different plug?
Yes, as you said, same fitment just different style plug.
Yes, if you have a bad coil, the misfire will move to the cylinder it is moved to.

That's a good thing, because it tells you which igniter is bad.
So, what would happen is IF you initially got a CEL P0303, and if you move the igniter to cylinder #1, then you would get a CEL P0301, etc.
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Old 03-23-2018, 11:19 AM   #19
sililis
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Quote:
Originally Posted by Samurai Jack View Post
So, what would happen is IF you initially got a CEL P0303, and if you move the igniter to cylinder #1, then you would get a CEL P0301, etc.


I am no longer getting a CEL for a misfire on cylinder 3 anymore. I went WOT after I checked all of the connections and gaps yesterday, even then nothing on the CEL. I think what I will do is buy a coil, then switch that around starting with cylinder 3.
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Old 03-29-2018, 10:25 AM   #20
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Quote:
Originally Posted by sililis View Post
A few days ago I noticed some very obnoxious bucking when accelerating above 1/4 of the pedal, so I ran to autozone and got a code about cylinder 3 misfire. Changed the spark plugs out yesterday and the bucking was noticeably smoother. I went and did a couple pulls on it to see if the issue was fully resolved but, lo and behold, when reaching around 4k rpm the bucking is there. Not as bad as it was before the plug swap but something is wrong here. Thoughts? By the way no cel is showing up.
At idle there is a very faint roughness to it as well, when picking up the girlfriend from work before I changed the spark plugs it did get very rough, but not since then, which leads me to think a possible bad MAF sensor? Will be buying a new fuel filter to rule out s**t gas just to ease my mind, not sure how to go about this one. Thanks.

EDIT: Boost is no longer going to appropriate range, only going to 7 psi.. which means there is a probable fault in the vacuum lines or bcs I believe, correct me if I am wrong. Are these two problems correlated? I did mess with the blue cylinder shaped apparatus(what is this?) to get at the passenger side spark plugs and noticed the line going to the tmic was loose, so I tightened it up a ways. Car is acting like I never changed the spark plugs I will have to wait until saturday to check anything unfortunately.
My 2002 wrx I was having this same problem with bucking, i would replace my plugs and it would go away for a couple weeks but then come back. And now i am really stumped... i went to replace my plugs because it started bucking again and it was bothering me. When i replaced the plugs the car started running worse, i cant even drive it, itís misfiring terribly and i have no idea what to think of because it was running strong and I replace plugs and now its running horrible
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Old 03-29-2018, 06:55 PM   #21
sililis
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Quote:
Originally Posted by Yamahaktm125 View Post
My 2002 wrx I was having this same problem with bucking, i would replace my plugs and it would go away for a couple weeks but then come back. And now i am really stumped... i went to replace my plugs because it started bucking again and it was bothering me. When i replaced the plugs the car started running worse, i cant even drive it, itís misfiring terribly and i have no idea what to think of because it was running strong and I replace plugs and now its running horrible
Have you tried replacing the coilpack(s)? I bought one today, will update on if this fixed my issue. No other ideas helped my situation, from IACV cleaning to new plugs or leaks, so I am hoping this is my golden ticket.

Any cels?
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Old 04-03-2018, 08:04 PM   #22
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UPDATE: After changing the coil pack on cylinder three, all is well. No bucking under acceleration! Thanks to all that helped me through this.
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