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Discussion Starter #1 (Edited by Moderator)
I've created this thread to highlight the most common fixes for any sort of 'Hesitation' issues commonly encountered with our Subarus. It seems many of us experience hesitation at some point in time and usually all for the same reasons.

Hesitation in this thread is defined as , but is not limited to : Throttle lag , Stumbling, and Bogging while the Engine is 'Under load'.


This hesitation may, or may not throw a CEL code. Most times, the hesitation is our 'early warning' of a part that is on it's way to failing,
and in a large majority of instances, no CEL's are thrown.

If you do get a CEL code, you can get them read at most auto parts stores.
(Auto Zone seems to be the popular choice.) Once you have a code, you can reference it here CEL Code Listing



**I have not arranged these 'solutions' in any particular order.**

Also : Most of these solutions will remedy hesitation problems at IDLE as well.


Common fixes for hesitation issues.

Oxygen Sensors

PCV Valve

Coil Pack (non-turbo)
Coil Packs (for turboed cars)

Spark Plugs

Spark Plug Wires (non-turbo)

Valve cover gaskets & Spark plug tube gaskets (Do this if you find ANY OIL AT ALL on your Plug wire ends, or spark plugs or, if you see oil in the plug tube.)

Dirty Injectors (seafoam cleaner)

Dirty Throttle Body (seafoam cleaner)

Dirty Electrical contacts on MAF or MAP sensors (Simply use Electric contact cleaner on the contacts. Do any you can find really,
it's not bad for them.)

Dirty or failing MAF or MAP sensors

Blocked, Clogged, or 'on its way to failing' Catalytic Converter

Coolant temperature sensor

And occasionally : Bad Gas

Also commonly suggested, is improving the Grounding under the hood.

The following are common sensors that fail in regards to the transmission ; causing hesitation problems, as outlined above.

TCM
Throttle position sensor
2-4 brake duty solenoid
ATF temperature sensor
Line pressure duty solenoid
Control valve
2-4 brake
2-4 brake timing solenoid
Speed Sensor
Lock up Clutch (4eat)
Tourque Converter (4eat)
Valve Body (not sure how it works or fails, but can cause issues)
Failing Clutch's
Gears
Clutch packs
Failing Differentials

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I will continue to update this thread as more information gets posted by you, the reader, or as new solutions to hesitation issues are found.
The somewhat sad irony of this thread is, I'm currently troubleshooting my own 'hesitation' issues, at this point, to no avail. My hope is that through my reasonable diligence, that others don't have to go through all these steps as I have.

If you have a solution to hesitation that you do not see posted, please post and I will add it. If you have links to DIY threads, or any other technical resources that relate, please post them and I will add them.

Thanks everyone! And Good Luck on clearing up your hesitation issues!
 

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I am having hesitation problems and idol problems in my 98 2.5. I beileve it is the throttle position sensor but i'm not sure. is there any way to check? (besides diagnostics.) I also read that when installing a throttle position sensor you need to adjust it to idol correctly, is this true?
 

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2000 2.5 RS
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I have kind of a wierd problem, and I'm having trouble determining if it's normal operation or not. I have an 00 rs with 120k miles on it. The problem really only happens in second gear. If I'm driving at 2krpm or higher, and release the gas pedal and let the rpms drop, ever single time it hits 1500rpm the car starts rocking back and forth, or bogging. after it drops below 1500 it stops. I originally thought that the car's just not meant to drop to that low rpm but the bogging is pretty excessive. No CEL currently. Any ideas?
 

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Discussion Starter #7
Not that I want to discourage you folks, but this is a sticky post.. not really the place to ask for advice or help troubleshooting your problems. They'd be better served, and better seen if you make your own post about your issue in this forum.

I appreciate the bumps, and thanks for reading! And please if you find a cure for your issue, please then post here and let me know what the solution was so I can cross reference them with our compiled list and add your solutions if we don't have them already.

Thanks guys! Good Luck!
 

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My car has been having slight problems with hesitation at idle. I cleaned my idle air control valve today with some denatured alcohol and q-tips and it idles much smoother now.

Here's where it's located on an EJ18 (and maybe EJ22 and 25 too?)
what is denatured alcohol, and could you post a few more picks detailing more specifically what you did ?

thanks
 

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2017 STi
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THANKS FOR THIS THREAD!!! I have been trying to figure out why my subie was hesitating during acceleration and your thread helped me out big time. I have already changed my cat, my sparkplugs, oxygen sensors changed, had my clutch replaced, headgasket replaced and some electrical work all to no avail (lot of $$$ too) (Valve cover gaskets & Spark plug tube gaskets Do this if you find ANY OIL AT ALL on your Plug wire ends, or spark plugs or, if you see oil in the plug tube.)<----- My mechanic did tell me that I have this issue and it would cost $150 to fix, I hope this is the cause. Time to get off the wallet. THANKS ALOT BRO!! much appreciated in PGH.
 

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2002 OBS, PSM/gsm
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24 Posts
just an idea...
since there are so many possibilities for this thread it might help out if we were more specific with our problems/solutions. i guess i'll start off with my problem as my example.

car: 2002 outback sport (auto)

relevant mods: ebay CAI, rallitek EL headers to full catless 2.5" system.

CEL code: just the emissions one.

symptoms: i have two types of hesitation. the first is right off of idle when i first open the throttle. the car feels like it wants to die for 1-2 seconds then it takes off as if nothing was wrong. the second hesitation is at freeway speeds (60-70mph or ~3000rpm) at 1/3 throttle. most of the time this is going up a hill while i'm holding the throttle steady the power delivery will waver. it's not a lot, but enough to make me worry.

solution: ....anyone have an idea? i really don't know where to start.
 

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99 Subaru 2.5 RS ..Gray
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57 Posts
same here man. i just replaced my ign coil, wires and plugs.. idk where to go next. some said fuel pressure regulator.. but idk
 

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2002 OBS, PSM/gsm
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okay... so i know i should've posted this a LONG time ago but i fixed my hesitation probs by replacing both O2 sensors, spark plugs/wires, fuel filter, and cleaning out my PCV.

i did all of them at the same time so i never ruled out and found the source of the problem. i wouldn't guess the issue was coming from the rear O2 sensor considering it's only for emissions. i only replaced mine trying to get rid of the CEL code (and it was pretty haggered from running catless).
 

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serenity now
AW 99 2.5rs, LRP 11 wrx
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i have a really bad hesitation

car: 1999 impreza 2.5rs 2 door 5 speed

mods: ebay shi, cobb double adjustable short shifter, no muffler

symptoms: really bad hesitation throughout the power band at 5000 rpm its like it hits the rev limiter and will not rev any higher. i am way down on power, and this might be irrelevant but i have white smoke out the exhaust, but i just had my head gaskets replaced. i took it to a master tech at the subie dealer and after 2 days he found nothing, so i took it to mac and the recommended plugs and wires so i did that and 44K and nothing has changed.

little help.
 

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After months of hesitation, my issue is resolved. I too changed plugs (champions, first, bad idea), wires, both 02 sensors, added seafoam, pvc valve and fuel filter. After the knowledge gained from here, I replaced the champions a 2nd time with NGKs. There was oil on the new plugs. The car ran like new after the new plugs and I added some of the thick oil additive that stops leaks. Drove to NC and back, around 1500 miles and have had no problems yet.
 
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