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Hesitation? Look Here First!:

282K views 201 replies 92 participants last post by  02OBS25L 
#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

_______________________________________________

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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#3 ·
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?
 
#4 ·
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?
 
#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!
 
#13 ·
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.
 
#14 · (Edited)
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.
 
#17 ·
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).
 
#18 ·
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.
 
#42 · (Edited)
EXACTLY my issue. Like a hit a freakin rev limiter at 5k.. Did you ever figure out what your issue is?

I'll elaborate a bit more - From a stop, if I go straight to WOT it will bog then rev up. seems like it has ok power from 1 to 3500 to 4k then after that, revvs SLOW and at 5K under load (fwy, WOT) feels like a rev limiter, will sometimes go above then it hits the phantom 'limiter' again.

Just changed the front o2, im going to try the rear and the normal tune ups. Any other suggestions?
 
#19 ·
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.
 
#21 · (Edited)
Dont worrie, found out what caused it.. :)
I was enquiring about an UNICHIP Q for our engine (nice results but very expensive)
With a piggie back, he said "youd be getting an extra 18-20kw atw and an extra 16% torque; all accross the range."
Thats 133kw [~90-100 atw] and around 235nm atw
Mind you this is with the AU shitty ECU putting 113kw stock...Far from the US 123kw
Still, nice gains :)

Back to business..
Before I even described the problems, he told me the problem with our engine and mods..
He said when our cars get exhaust and or intakes, the fuel maps cant keep up..
This causes the hesitation we find at launch and between 3-4k.. :D
 
#39 ·
Before I even described the problems, he told me the problem with our engine and mods..
He said when our cars get exhaust and or intakes, the fuel maps cant keep up..
This causes the hesitation we find at launch and between 3-4k.. :D
Anyone have any input on as to whether this is tied to the Australian ECU or if it extends to the US ECU also?
 
#22 ·
Im kinda repeating myself here, but it needs to be said :D

Ok, believe this or not..
Over the past couple days, I got fed up with my cars performance..
I would lug around, bog on take off, hesitate between 3-4k
So after reading some hesitation threads, I went on a quest to solve mind.
(Some solutions suggested leads, fuel fliter, use of suby cleaner, bad sensors.. anything and everything)
While in a quest to solve this, and subsequently get more performance.. I had a look into Unichips.
After extensive research, and mainly a few phone calls I discovered something..
It turns out, our ECU's cant realy cope with alot of modding (Without tuning)
Theres not much of a tolerence for an increase of air and flow, lord knows why.
After further research, and speaking to my stepdad (Ex-Mechanic) He explained that with harleys [and apparently N/A subarus] you can do one and not the other (exhaust/intake)
given I had a full exhaust, I decided to whack back on my standard intake.
FK DID I GET A SHOCK!
The car pulled like a tractor from 1k-redline!!
The mechaics from Unichip explained that the fuel maps were the culperate, and if I want acctual gains out of an intake.. it NEEDS to be tuned.
If you have a full exhaust, please.. for the sake to 20minutes!
Go back to your standard intake, rezys and all!
I was expecting to have the same issues, and have to spend countless hours and money trying to fix this..

I couldnt be happier! :)
 
#25 · (Edited)
To follow up on that, I have proof that the intake is the culperate for our hesitation.
http://i201.photobucket.com/albums/aa93/jaydnisevil/SCAN0026.jpg
Red line was with full exhaust + UEL headers and stock intake.
Blue line was with the back of the airbox disconnected (pannelfilter just held in place over the TB)
Keep in mind this is an EJ251 MAP NOT MAF!
Australia only got 150hp engines and the US got the full 165. From what iv heard, that was just down to tune differences between MAP and MAF.

NOTICE how the power and torque is increased down low!! Contrary to popular belief, its only the midrange that is effected (3k-4.5k)
 
#26 · (Edited)
The "on the freeway, 1/3rd tnrottle, up a hill" sounded like silent detonation witch points to a lean fuel diagnosis, but I think Jay, or more directly the chip maker and his father said, it's probably a subie built in programming issue. If your built in meters (MAF or MAP) are designed to give an output of 0.00 to 1.00 and the subie programmers disigned it under stock use to hit .95 at full trottle with our stock restricted intake and exaust, then it only makes sense that increasing your intake or exhaust can top out the meter. Now since the meter is topped out it's no longer delivering enough fuel for the amount of air coming into the engine.
Thanks jaydnisevil, I learned something new about my soobie today
 
#28 ·
MY problem

My 97 impreza L 2.2L hesitates when i give it gas really quick. it starts to bog and inch forward, even with the gas to the floor. this happens when i pull out of a road or try and accelerate quickly from a stand still. its almost got me hit a couple times please help me, here is what ive done so far with no success.

p.s its been doing this since i got it!!!

-changed plugs, wires, & coil pack
-changed fuel & air filters
-cleaned injectors and throttle body with sea foam, gum out, & Lucas fuel treatment
-changed alternator
-changed downdraft o2 sensor

any suggestions, does this sound familiar?
 
#30 ·
My 97 impreza L 2.2L hesitates when i give it gas really quick. it starts to bog and inch forward, even with the gas to the floor. this happens when i pull out of a road or try and accelerate quickly from a stand still. its almost got me hit a couple times please help me, here is what ive done so far with no success.

p.s its been doing this since i got it!!!

-changed plugs, wires, & coil pack
-changed fuel & air filters
-cleaned injectors and throttle body with sea foam, gum out, & Lucas fuel treatment
-changed alternator
-changed downdraft o2 sensor

any suggestions, does this sound familiar?
When you say downdraft o2 sensor, which one are you speaking of? The o2 sensor that affects the a/f ratio is the one closest to the headers.
 
#29 ·
I recently spoke to another tuner, they said the ideal exhaust size for our cars is 2" mandrell.. (Without a tune of course)
He described our symptoms very similarly to the previous tuners Iv spoken with.
Bog on initial throttle, but as it gets going things start to get moving.
I find that after 1/4-1/2 throttle the car just doesn't accelerate any harder :(
Without a tune, our ecu's have a hernia with any major mod.
I posted 'lonley drivers' piggyback vs un-tuned previously, and you can see the mid range bog disappears. Its a shame, but im thinking its the cause for all our problems :(
 
#31 ·
i ment the one on the rear cat. the one closest to the back of the car.

i didnt know the one closest to the engine affected the air/ fuel ratio ill have to change it too. i changed the other o2 sensor because it was throwing up a CEL.

if that doesnt work, do you have any other suggestions?
 
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