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Old 06-25-2022, 12:59 PM   #1
KeithS05RS2.5
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Default Bucking / Misfire / Hesitation under WOT boost - Thoughts?

Hey guys I just wanted to throw this thread out there to get some input on what you guys might suggest may be going on with my 02 WRX. Car was off the road for 6 years and I just got back on the road again. Ive been driving it for about 3 weeks with no issues at first.
Slowly a hesitation issue has been building this past week and has gotten to its worse point last night

Im getting a serious stumble or misfire when entering boost under WOT. No codes, no flashing CEL, I spent some time trying to isolate the condition and this is what I can report:

It is most violent when cruising at highway speed in 5th .. say 60mph .. and then downshifting to 3rd (passing a car for example). If I downshift aggressively and go WOT the car bucks violently ( exhaust sounds similar to hitting limiter) until I pull my foot off the gas a little ... say 75% throttle ... then everything cleans up and I can go 100% throttle and it enters boost strong all the way to redline

If I do the same scenario but only drop to 4th, there is a very slight hesitation as it enters boost but then cleans up on its own and boosts strong until redline

Same scenario, but leave it in 5th and go WOT it slowly enters boost with no noticeable issues.

Last scenario: WOT pull from a dig. 1st pulls strong all the way to redline. 2nd seems normal and strong all the way to redline, 3rd there is a slight stumble, but it clears up without back out of the throttle all the way to redline, 4th same hesitation entering boost the clears up on its own and boosts strong to redline.

After doing some research Im going to start my cleaning the MAF first, as it is a next to $0 cost to try

If that doesn't work Ill try new plugs (current are 8 years old with only maybe 3k on them)

Then maybe try coil packs, current are the OEM originals


Just wanted to see if anything specific jumps out to you guys based on the scenarios above, any input is greatly appreciated.


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Old 06-25-2022, 01:21 PM   #2
hybrid gti 2
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Most of the time when you have the WOT and spitting is a A/F issue. Common thing would be to check the plugs. Then look at any leaks vacuum and turbo inlet. Also you have to consider the tune and where it got tuned. Say if you moved several states away and had an elevation change and such. There are many threads on misfire issues from wiring to coilpacks. Yet WOT is generally a A/F issue, generally 3/4 to WOT. If it was me I'd look at some new NGK and gap them more toward the minimum to give a stronger spark, like 0.028 gap.

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Old 06-25-2022, 01:30 PM   #3
KeithS05RS2.5
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Quote:
Originally Posted by hybrid gti 2 View Post
If it was me I'd look at some new NGK and gap them more toward the minimum to give a stronger spark, like 0.028 gap.
Yea, if MAF cleaning doesn't change anything then that's what Ill do. I went with 1 step colder NGKs way back when I did the E-tune, I was under some misinformation that iridium's don't need the gap checked, so I never checked the gap before putting them in.

Only thing that makes be scratch my head is why the car was driving great for a while and then developed the miss. I would think that if it were a poorly gapped plug it would have been present when I first put it back on the road
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Old 06-25-2022, 01:57 PM   #4
LAS04subie
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I’ve had some similar issues with my 05 wrx. Make sure all your grounds are clean and secure. Could add a couple of extra grounds. Since it’s at wot probably won’t be this but the idle air control valve can be cleaned also make sure to get a new gasket if you open it up. Check your oil level. My car was acting up one time because I was low on oil.


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Old 06-25-2022, 04:03 PM   #5
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Quote:
Originally Posted by LAS04subie View Post
Make sure all your grounds are clean and secure. Could add a couple of extra grounds. Since it’s at wot probably won’t be this but the idle air control valve can be cleaned also make sure to get a new gasket if you open it up. Check your oil level. My car was acting up one time because I was low on oil.
Ill add checking the grounds to the list. Battery has been relocated to the trunk, so double checking cant hurt
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Old 06-25-2022, 07:36 PM   #6
hybrid gti 2
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Common misconception that the gap is good out of the box. Auto parts stores love to say that but for suby's they are a bit more needing to have the plug gap on point to maintain the correct a/f. Maf is always a good place to start, yet if you have a leak after the maf it will cause issues with not having the correct a/f, depending on how big the leak is. I've found leaks at the throttle body gasket, turbo inlet, y pipe gaskets on the tmic, and the bov gasket. But most of the time with bucking I found it was related to plug gap, unless it was tune related. On gaskets that I wasn't going to re-vist often I would silicone them, like the y pipe. Hopefully you get it solved GL

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Old 06-30-2022, 02:18 PM   #7
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Lots of threads with this same issue. I've run into it multiple times as well.

What fixed mine after exhausting all other possibilities was replacing all the coil packs. If your car is old then new coilpacks is a good idea anyway. NGK coilpacks from RockAuto aren't that expensive and as good as OEM. Don't cheap out on these.

Here is my list of things to check:
Check all your grounds and battery terminal connections.
Add grounds.
Change plugs and check gaps, make sure plugs aren't loose.
Boost Leak test.
Check vacuum lines.
Check fuel pump and fuel pump sock.
Change fuel filter.
Could be bad fuel pressure regulator.
Replace MAF.
Replace BCS.
Replace alternator.
Replace coil packs.
Replace coil pack connectors.

Tackle the easiest things first.
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Old 06-30-2022, 02:36 PM   #8
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Mine was coil packs, the 2020 black sti coils are same as gray, same dwell map, but u can get pull offs with 10k miles cheap
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Old 07-04-2022, 08:47 AM   #9
KeithS05RS2.5
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Thanks guys.
This happened right before I went on vacation for a week.
Im back now and will start trying some things in the next couple days.
Ill post what worked and what didnt.
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Old 08-30-2022, 09:47 AM   #10
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Quote:
Originally Posted by KeithS05RS2.5 View Post
Thanks guys.
This happened right before I went on vacation for a week.
Im back now and will start trying some things in the next couple days.
Ill post what worked and what didnt.
Hi, did you ever find the issue?

I realize this post is about 6 weeks old.. I'm trying to troubleshoot an 04 WRX that appears to have a fuel related issue. (And I need to reply to a few posts before I can create a post of my own...).
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Old 08-30-2022, 11:19 AM   #11
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That old of vehicle, I would point to coil packs of all other bases have been covered

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Old 08-30-2022, 03:24 PM   #12
KeithS05RS2.5
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Quote:
Originally Posted by haggar1850 View Post
Hi, did you ever find the issue?

I realize this post is about 6 weeks old.. I'm trying to troubleshoot an 04 WRX that appears to have a fuel related issue. (And I need to reply to a few posts before I can create a post of my own...).
Sorry, Ive been a little lazy getting to working on the car. I did clan the MAF and it did eliminate the bucking and misfire but I can feel when WOT everything is not 100%
I have new plugs to go in this weekend to see if that changes anything
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Old 09-06-2022, 06:57 PM   #13
monkeyposeur
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At this point I would get a new MAF. They stop working 100% as they get old. Find the Denso part number and you can order one on Amazon for a lot less than the dealer.
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Old 09-07-2022, 02:50 PM   #14
KeithS05RS2.5
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Quote:
Originally Posted by monkeyposeur View Post
At this point I would get a new MAF. They stop working 100% as they get old. Find the Denso part number and you can order one on Amazon for a lot less than the dealer.
The MAF is only about 6 years old. I replaced it before I initially had the car tuned. Probably less than 10k miles on it.
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Old 09-07-2022, 04:22 PM   #15
monkeyposeur
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Quote:
Originally Posted by KeithS05RS2.5 View Post
The MAF is only about 6 years old. I replaced it before I initially had the car tuned. Probably less than 10k miles on it.
Ah, Ok. Good luck with this man, it seriously is the worst.

Have you checked this thread out? - https://forums.nasioc.com/forums/sho....php?t=2403736
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Old 09-09-2022, 03:21 PM   #16
KeithS05RS2.5
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Quote:
Originally Posted by monkeyposeur View Post
Ah, Ok. Good luck with this man, it seriously is the worst.

Have you checked this thread out? - https://forums.nasioc.com/forums/sho....php?t=2403736
I just did ... makes me think a bit ...

I did have to extend the wiring harness for the MAF. I remember the first time, I did not properly connect the shielding back together and had to redo it. Wonder if it may be a gremlin from that. Ill add it to the list.
Unfortunately Ive been so short on time lately that I may not get this diagnosed before I have to put it up for the winter lol
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Old 09-18-2022, 07:22 PM   #17
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Got the fresh plus in today...
Could have sworn I went with 1 step colder NGK iridums

But the part numbers showed they were 1 step colder coppers, and were gapped to a pretty loose .030

Two of the new iridiums were a perfect .028 and two had to be gapped down from a tight .030 to .028.

I cant feel any more sign of hesitation of missing during boost which is great.

But there is still this feeling like the car is struggling to build boost mid rev range in 3rd gear. Ill do a boost leak test next just to make sure.

Also something frustrating I noticed ... my tune is set for a peak boost of 20psi.
My AEM boost gauge shows that I am hitting target boost, but when its showing 20 psi on my gauge, the Accessport is only showing 16-17psi??
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Old 09-18-2022, 07:22 PM   #18
KeithS05RS2.5
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Got the fresh plugs in today...
Could have sworn I went with 1 step colder NGK iridums before

But the part numbers showed they were 1 step colder coppers, and were gapped to a pretty loose .030

Two of the new iridiums were a perfect .028 and two had to be gapped down from a tight .030 to .028.

I cant feel any more sign of hesitation or missing during boost which is great.

But there is still this feeling like the car is struggling to build boost mid rev range in 3rd gear. Ill do a boost leak test next just to make sure.

Also something frustrating I noticed ... my tune is set for a peak boost of 20psi.
My AEM boost gauge shows that I am hitting target boost, but when its showing 20 psi on my gauge, the Accessport is only showing 16-17psi??
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