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Guest Message by DevFuse

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Subaru Hesitation Problems

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81 replies to this topic

#26 Guest_Bagheera85_*

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Posted 11 December 2001 - 08:39 AM

I'm thinking the board is getting confused lately.. replies seem to just pop up in other threads...

#27 Guest_Azulan Chaosbreaker_*

Guest_Azulan Chaosbreaker_*
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Posted 04 January 2002 - 11:50 AM

I have 2002 Legacy Outback 5-speed with 3,000 miles that has a hesitation problem at low RPMs. It is most noticeable in stop and go traffic when trying to maintain speeds of 5-10 mph in 1st gear. The vehicle will not accelerate/decelerate smoothly lurching forward and then back as the engine kicks in and out. Slipping the clutch helps, but this isn't fun, nor good on the clutch. Accelerating from a fully disengaged clutch at close to idle speed also results in a hesitation before the engine "kicks in" with is very noticeable while turning in front of on coming traffic--I only tried this once. Higher RPMs and more slipping of the clutch gets me around the problem, but again this can't be good on the clutch.

I have service appointment on Monday to have this checked out, but these "soft" problems are sometimes hard to deal with if dealer is uncooperative or if it is a new problem for the service department. Are there specific items that I could present to the dealer to have checked?

I should note that I have never owned an automatic so I am use to driving a clutch, and haven't experienced a similar problem in 5-speed Hondas and VWs. This is my first Subaru.

#28 Guest_meep424_*

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Posted 04 January 2002 - 12:22 PM

Sounds more like bucking than hesitation. Mine is prone to do this too...I sometimes have to dump the clutch and "try again." First gear is so strong in these cars, and the engine has so much torque, that I think it's just really, really sensitive....the motion of the car jumping forward pulls the gas pedal away from the foot, causing it to rapidly slow, whereby your foot finds a bit more pressure against the pedal (you just got lurched forward) causing the car to again lurching forward, etc..... at least that's what I experience. And the car is so sensitive in this gear and speed that I do think it's more the driver-car relationship than the car (at least in my case).

To counter this what I'll do is get into 2nd quickly if I'm in that kind of traffic. 2nd seems good down to 5 mph if you're gentle.


#29 Guest_kmix99_*

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Posted 04 January 2002 - 08:42 PM

Haynes does a good job in explaining how to check and adjust the TPS. All you need is a volt meter, feeler gauge and a phillips screw driver. Be careful not to strip the screw heads (like I did) when loosening the sensor--- not fun to drill out.

Mine was slightly out of adj--- seemed to shift better after adjustment.

#30 Guest_trayborcret_*

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Posted 05 January 2002 - 12:21 PM

My 89RS legacy suffers from hesitation which I subsequently got code 22 from the ECU telling me it's the knock sensor. I've been awaiting the new one now for some time and whilst waiting the car has begun to deteriorate. Basically seems to be worse when it's cold, at between 2000 & 3000 rpm when cruising, not accelerating it splutters, jerks, and cuts out a lot until I put my foot down more.
Almost like when you go for 3rd gear and hit 5th by accident but the engine isn't struggling in that sense. Hopefully the knock sensor will sort it but I'd like to rule out various other things. It's running without the sensor on at present but I presume this is only the same as running with a dodgy/broken one?
I'd like to try cleaning the TPS but don't have any reference material to see what/where exactly it is. I'm not worried about stripping it to clean it as I'm plenty capable of doing my own work, I just don't know where it is. If anyone has a picture etc or details about cleaning it I'd be most grateful!


#31 Guest_Legacy777_*

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Posted 05 January 2002 - 03:40 PM

Jim check out this thread pub1.ezboard.com/fultimat...D=36.topic

Should help ya out.

#32 Guest_trayborcret_*

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Posted 06 January 2002 - 02:25 PM

Thanks Josh - will do!

#33 Guest_PaganQWA_*

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Posted 06 January 2002 - 02:42 PM

My wife's (funny how its her's when im describing something bad and its mine when im talking about how great it is :lol: ... i dont feel bad though, its suddenly my car when something brakes :P anyway) 1990 Legacy L wagon (EJ22 engine, auto 4 speed, 2WD) has bad hesitation. If I dont gently push the throttle and let it come up at its own pace, it will just bog down. If I mash the gas it bogs down for a second then sputters upto 3000 RPMs... above 3k I runs just fine to me. Maybe the higher RPMs are masking the problem or its actually only a problem at low RPMs... i dunno.

I think the manual masks the problem becuase you can down shift and use the clutch to throw more power at the problem and mask it. I notice if I manualy shift the the AT I can mask it mostly but its definatly still there. I can just keep the RPMs near or above 3000 so the hesitation/bogging isnt noticable. Unfortnatly thats not a feasable work around with an AT :(

Just thought I'd share my experiences :)

#34 Guest_fldcar_*

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Posted 06 January 2002 - 09:04 PM

I have hesitation probs in my 90 legacy too, I can not seem to find the culprit, Mine happens right around 4000 rpms, It is smooth up to 4K and then the tach seems to just freeze in place for a split second and then it is smooth all the way up to 6500, I think it may be the TPS, Is there a way to actually open the TPS and clean it? This is the only thing I can think of, It has new plugs, fuel filter, air filter, Pcv and etc.


#35 Guest_Legacy777_*

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Posted 06 January 2002 - 09:08 PM

Yes, you can open the TPS and clean it....you can also test it. Here's the link to the info pub1.ezboard.com/fultimat...D=36.topic

I'm goin to try and do this next weekend. Picked up some electronics cleaner.

#36 Guest_Roadsplat_*

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Posted 06 January 2002 - 11:22 PM

I had the hesistation problem too. However, I have a 97 OB 2.5l and the TPS is a sealed unit and cannot be cleaned. I did adjust it and it helped with the shifting hesistation. However, it seems that my gas mileage has decreased since doing it. Does any one know, if I did screw up on the adjustment , could this affect my gas mileage?

Thanks for any info.


#37 Guest_trayborcret_*

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Posted 07 January 2002 - 07:16 AM

Makes sense that it would mess up the fuel mixtures as I think that's what the TPS is largely for: so the ecu knows what mixture to provide depending on throttle position. I think that's the general idea anyway!

#38 Guest_Bagheera85_*

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Posted 07 January 2002 - 12:38 PM

When cleaning, do you take the cover off the tps? If so, how?

#39 Guest_Legacy777_*

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Posted 07 January 2002 - 02:13 PM

I will post details of my experience of the TPS cleanin after this weekend....that's when I'm planning to do it.

#40 Guest_bigmikeb_*

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Posted 11 January 2002 - 02:21 PM

Thank you. I have a 2000 Legacy Outback Wagon. Bought it in June with 33,000 miles on it. I loved it until
the hesitation started! At 52,500 miles! It actually just started a week ago. They plugged it into the computer and told me I needed a new coil pack; which I bought and replaced.... It was great for 3 days!
Today, in the rain, it started up again. Rain stopped. Hesitation stopped! I just posted a "pleading"
on this website - begging for help. Found this posting and it sounds like me! I just got off the phone with the NHTSA. Thank you Subaru people.

#41 Guest_yushincho_*

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Posted 12 January 2002 - 01:57 PM

Hi all,

From Jan. 10, my 96 impreza, manual shift, 1.8L starts to fluctuate suddenly.
I suspected the oil change(engine oil, manual gear box and rear diff. gear with GL5 75W90) done on Jan. 9.
But about 45 miles and 36 hours just after oil change, it was really ok, no problems experienced at all.

The hesitation, I can describe it as forward/backward fluctuation starts suddenly.
The symptom is;
1) Over all gear range(1st ~ 5th), fluctuation happens intemitently, but a bit often, every 5~10 minutes.
2) Fluctuation is in the way that fuels does not come to engine and after 3~4 seconds after I accelerate it pushing the pedal.
3) Fluctuation happens even in the idle state, netural gear position. But it happens during the stop for light, not at the first I start the engine.
4) It happens more at the RPM(1500~2500) than at RPM (2500~3500)

I think it is very similar to those symptoms of Itzik93 and Azulan Chaosbreaker.

Thanks in advance for any comments or helps.

#42 Guest_yushincho_*

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Posted 12 January 2002 - 09:09 PM

I've got another information that hesitation happens just after engine oil change.

Following is extracted from
"<a href="http://www.geocities.com/hobiegary/hesfix.htm"">www.geocities.com/hobiegary/hesfix.htm"</a>
and "<a href="http://www.geocities.com/hobiegary/hesitation.htm".">www.geocities.com/hobiega...tion.htm".</a> Where, some guy is selling fix kit.

Hope to hear your opinion about this.

Why after oil changes?

It has been recognized by many that hesitation normally starts following an oil change. Why? Most authorities on this phenomenon agree that the knock sensor is reporting sounds to the ECU that come with the engine pumping up a new oil filter. When a new filter is installed, it is full of air and not oil. When the engine is started, the oil pump is pushing oil in and air out of the new filter. This creates subtle sounds that are normally not heard by the ECU. It also provides a short delay of lubrication being delivered to the rest of the engine as the air passes. This also causes the engine to be noisier than usual.

The electronic fix will muffle the effect of these and other ambient noises to allow the knock sensor and ECU to react more exclusively to genuine engine knock, pre-detonation sounds.

And my understanding on hesitation is:
A knock sensor is misinterprete 'the air pumping sound from new oil filter' as 'uneven burn and knocking sound from the engine' . And this will control(decrease or delay(=retard?)) the amount of fuel to engine.

And for your reference,
the Knock Sensor is doing below.

The knock sensor senses when fuel is burning unevenly and causing "knocking" or irregular vibrations in the engine. It consists of an electric coil that is wound around two ceramic rods with a magnet in the center. The vibration of the engine causes the rods to vibrate. This disturbs the coil’s magnetic field and alters the current passing through the coil. This disturbance returns to the computer as a signal pattern that the computer analyzes. The computer then determines whether the vibrations are characteristic of engine knocking.

Hope all having this problem solve it away!

#43 Guest_Legacy777_*

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Posted 12 January 2002 - 10:37 PM

Yeah....I've run across Gary's site. I tried his electrical fix, didn't like how it worked.

#44 Guest_yushincho_*

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Posted 13 January 2002 - 12:41 AM

I appreciate telling me your experience, Josh.

Hearing your experience on Gary's fix, I think I'm getting away from the simple and easy solution to cure my problem.

Feels like that I need to be more struggling on this...

Because I got this impreza last October and it was ok for last 3 months. Though the maintenance of previous owner could be so bad, I don't think so-old spark plug or wire can abruptly make this situation(lurch the engine or hesitation about 3~4 seconds)

I just bought plugs and wires, but I think it's a good idea not to replace it before I solve this problem. Because I also expect the cause is from several sensors and ECU, not from old spark plug or wires.

My problem is very serious, I think.
It made me so nervous and even scarced at high speed.
I couldn't accelerate from 45mph to 55 or 60 mph to merge a highway.
At first, I suspected the manual transmission oil and rear diff. oil since I felt something is wrong with power shift between front and rear. BUT, it happens at idle, netural gear position !

I'm gonna detatch the TPS and see if it is really dirty and
measure the resistance of it.

I had no problems at all with my previous 92 Legacy Sport, AT except rusty wheel house, which made me sold it away.

Yushin - '96 Impreza, manual, 1.8L, 78K mile

#45 Guest_Bagheera85_*

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Posted 13 January 2002 - 09:12 AM

Just a thought.. but the knock sensor would send voltage back to the ECU right? If this is the case, then a small resistor to drop the voltage slightly would theoretically help the situation, in and overly sensitive knock sensor, no?

#46 Guest_trayborcret_*

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Posted 13 January 2002 - 09:24 AM

I think that's the idea of the kit that you can buy from the website. In theory yeah it'd work, but you would have to bear two things in mind: a) That the resistor was a suitable value, B) That it would potentially mask genuine knock problems.

#47 Guest_Legacy777_*

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Posted 13 January 2002 - 10:53 AM

well I have gary's little fix....it is a little more complicated then a simple resistor. I can try and take some pics of what it is this evening.

I'm personally leaning back towards a mechanical fix. I was trying to find material properties for different materials and find one with a few points lower value then aluminum was, but still have the ability to stand up with the heat and what not in the engine bay.

I really haven't been able to find any helpful data.

#48 Guest_Commuter_*

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Posted 13 January 2002 - 07:57 PM


What about some old (or new) gasket material? I'm thinking of something like a head gasket or exhaust manifold gasket. One of those that are a gasket material sandwiched in some thin metal. I have no idea how the material properties would compare, but it should dampen and take the heat.


#49 Guest_Legacy777_*

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Posted 13 January 2002 - 09:23 PM

hmmm, that's a good idea commuter.

#50 Guest_Gus_*

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Posted 14 January 2002 - 01:21 PM

I was thinking beef jerky.

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