throttle issues?

joshuah

Forum Member
Joined
May 3, 2009
Messages
12
Location
Kuranda, QLD, Australia.
Hi,
I'm going spare trying to diagnose this one!
Problem is with my MY02 Outback. The accelerator is very touchy. Releasing it just a fraction and the car loses all momentum, lunging me forward. Deperessing it again ever so slightly and she re-engages and takes up the slack quickly. There is no in between and reducing to a coast can not be done smoothly; in fact, it won't coast smoothly at low speeds, not even on cruise control.
When descending down hills in any lowish gear, just engine braking, she can buck and hobby-horse. Depressing clutch stops this...until the next time.

I have read that it may be an ECU problem, or engine/tranny mounts, Throttle sensor, anti-knock sensor... but no-one seems to know. Mounts seem ok, very little backlash in drivetrain.

I have already installed a 2nd clutch, which did nothing except cost me lots of $. The mechanics aren't too sure either, so I'm releuctant to spend more on it for no gain! Scanner indicate nil error codes.

Anyone else have such problems? How should I tackle it?
 
joshuah,

not sure if it is the way the computer is set for the fuel injection, or what, but our '05 Impreza does the same.

Beigewagon.
 
Sounds electronic - perhaps throttle control / idle control valves. Have a search over on subaruforester.org and ozfoz.

Engine does not return to idle.
1) Idle air control solenoid valve
2) Engine coolant temperature sensor
3) Accelerator cable (*6)
4) Throttle position sensor
5) Pressure sensor​
6) Intake air temperature sensor
 
sounds like an exagerated effect of the normal ecu operation - try reflashing the ecu (disconnect it over night)...
 
Hi,

She's got 175000km behind her. I do all usual servicing except timing belt, but a couple weeks ago, the mechanic cleaned the throttle body, which was apparently a bit grubby. It drives nicer but the problem remained.

Problems seemed to coincide with the installation of a new clutch to a single solid/rigid flywheel. The first one installed was a 'clutch pro' brand. Mechanics thought the spring was a bit weak, so they suggested installing an Excedy, which they did, but did not fix the problem. It's a better clutch and has a nicer feel, but that's it. Related?

I also read somewhere that Foresters had a similar problem in Canada and US which was fixed with a software upgrade. Is this likely in Oz? Are there bulletins of updates available online or similar?

Meanwhile, I have really adapted my driving style which has helped, but not in low gears. babying the accelerator and releasing it ever so slowly works a bit. Hopefully it'll reduce the wear drivtrain for a long as possible.

thanks for the input.
 
oh, and tried the ECU reset, installing a new stereo. Disconnected for a couple hours. Also put in a new battery to fix hard cold starting. This didn't work either. I think I need a new mechanic?
 
well if it coincided with the clutch /flywheel - I wonder if the flywheel is the culprit!? is it idling lower than before?
 
It's a new flywheel and they re-machined it before putting the Excedy in. The flywheel has done about 5000km all up.

It may actually be idling a little lower, around 600-700rpm. What does that tell you?
 
Im no mechanic but im thinking if its idling lower, and dropping revs quickly when off the gas, maybe their is some sort of friction against the flywheel (throwout bearing, clutch??) Not sure... maybe 'Rally' on here can chime in with some advice :)
 
I have an 06 Impreza that does similar also. There's a slight downhill stretch of road that I drive down everyday and it's impossible to keep a constant 60km/h (the speed limit) on this road. Throttle off and the car slows down, open the throttle the slightest amount and it starts picking up speed. It must really annoy drivers behind me!!

I'm thinking it has something to do with the interaction between the idle air control valve and injector cut. When the car is rolling the idle speed on mine always is above 1000rpm (coasting clutch in or neutral) it only seems to drop down below this if you actually stop (ie. no reading on vehicle speed sensor). Couple this with what I suspect is the ecu cutting the injectors at throttle off and your high idle suddenly gets cut as the fuel stops being injected, then the slightest touch of the peddle turns the injectors back on and the vehicle then takes off again on a high idle speed.

Anyway that's my theory on it and it's only a theory as such and still doesn't help that the car can be a PITA to drive in certain situations. The amusing thing for me though is the fact that my previous L-Series with multipoint EFI EA82T was much better behaved - and that was without the benefit of the subsequent 20 years of EFI development - lol.
 
Last edited:
Brain's a bit asleep after a night out, but have you checked the throttle cable is right? I had a scary moment once in my WRX when I floored it on the M4, and lifted off but the throttle was jammed wide open. I continued to accelerate at quite a rate (as you do in modfied WRX's on full throtttle) for a couple of seconds until I braked and turned off the engine and pulled over. The cable had become loose and binded- it had never been touched in years. Other things could be a faulty TPS or connection.


joshuah said:
Hi,
I'm going spare trying to diagnose this one!
Problem is with my MY02 Outback. The accelerator is very touchy. Releasing it just a fraction and the car loses all momentum, lunging me forward. Deperessing it again ever so slightly and she re-engages and takes up the slack quickly. There is no in between and reducing to a coast can not be done smoothly; in fact, it won't coast smoothly at low speeds, not even on cruise control.
When descending down hills in any lowish gear, just engine braking, she can buck and hobby-horse. Depressing clutch stops this...until the next time.

I have read that it may be an ECU problem, or engine/tranny mounts, Throttle sensor, anti-knock sensor... but no-one seems to know. Mounts seem ok, very little backlash in drivetrain.

I have already installed a 2nd clutch, which did nothing except cost me lots of $. The mechanics aren't too sure either, so I'm releuctant to spend more on it for no gain! Scanner indicate nil error codes.

Anyone else have such problems? How should I tackle it?
Click to expand...
 
Check TPS.....

Like Rally Stated....
Your Ride has 175k on it....things get worn with time, and the TPS gets ALOT of work over the duration of its life....

I had a 96 Outback with 160k on it Auto AWD....when I first got the thing it had very sporadic Shifting issues...I thought the TCU was at Fault...No codes.
I replaced the TCU....Didn't fix the problem....I was working as A Tech at my Local Subaru Dealership at the time....Having Subaru Diagnostics Computer at my fingers, I and 2 Senior Techs went and drove the car...
Same sporadic Shift and drive issues...Computer Showed No Faults and No codes...??????? So as a Collective Mind set ( 3 Subaru Techs ) we dicided it had to be a Tired Tranny....Clutches and baskets having slip issues...

I replaced the tranny With a Rebuilt unit, Same issues....:catfight:
I did notice my idle was a bit low, 650rpms or so, and if I had the Defroster on went into gear the thing would Almost die. So we plugged it into the computer and tried to reset all the Sensors to bring Idle back up...( this was after cleaning everything Egr,pcv,vacuum lines,etc.)
As soon as we touched the TPS sensor to adjust things, I got a code.
We checked the TPS parameters, and low and behold it was JUST BARELY OUT OF WACK at one end....:poke: :shrug:

Replaced the Silly thing , and The car drives Like a dream.....Mechanics have a saying ( Things Happen in 3's) after my Wagon gave us Fits, over the next 2 months we had 2 other cars come to the dealer with similar drivability issues...One was a Stick the other Auto....both ended up being a tired TPS...?

If it were me, I would get ahold of a Factory Subaru Service manual or get the Info you need from your dealer, All the Engine related Sensors can be checked statically on the car...The Factory Manual is going to give you the Best info, TPS will have static ( closed ) readings as well as WOT( wide open throttle ) Readings...I would investigate that as well as Idle air control Valve,and both your throttle cables, Main and Cruise....
If one of these is too tight, it will cause issues as well...I do a finger test

With your Index finger you should be able to push down from the top of each cable at the throttle body and get 1/8-1/4 inch of play before the throttle plate begins to move.....You want to verify the Throttle plate is Bottomed out at idle, if it is not, this can cause the TPS to read things wrong....

Hope this gives you better food for thought....Let us know what it ends up being.....:iconwink:

John.
 
Sourcing late model factory service manuals

subaruguy72 said:
... If it were me, I would get ahold of a Factory Subaru Service manual ... The Factory Manual is going to give you the Best info, TPS will have static ( closed ) readings as well as WOT( wide open throttle ) Readings...I would investigate that as well as Idle air control Valve,and both your throttle cables, Main and Cruise....

Hope this gives you better food for thought....Let us know what it ends up being.....:iconwink:

John.
Click to expand...

BUT Where on G*ds earth does one get a factory service manual? :twisted::twisted:

I'd happily pay for one for my 05OB, but they just can't be had!
 
PM Hondaslayer (Ben at Hodges Subaru)
 
Hmmm. Think I'll be checking my TPS as its behaving in the same manner as described here.

As for the manual issue, the factory manuals are hard to find at best but the Haynes or gregory (same company actually) manuals do the job good enough. What they don't tell me I make up/work it out myself...

Cheers

Bennie
 
Well I checked the TPS on my EJ22 this arvo, this is what I got:

The on off switch (off at throttle closed, on at everything else) checked out ok. I need to find a set of feeler guages to check the change point of this at set throttle opening invervals.

The voltage at different openings of the throttle is meant to be 0 to 0.5 volts at throttle closed, as the throttle opens it should head up to about 5 volts at full open throttle. Reference voltage should be about 5 volts, I got 5.15v.
The voltage readings are all backwards. I'm getting 4.8something volts at closed throttle and about 0.1 at full throttle. So I'm guessing there's something wrong there. I've got a second unit at home in the shed that I'll be checking tomorrow after work, which ever is the better unit will be the one that ends up on the motor...

Any thoughts on those readings?

Cheers

Bennie
 
On my MY99 WRX- and I imagine Subaru would use similar principles on other models, voltage at fully open is 4.3v + or - 0.3v, and fully closed 0.5v + or - 0.3v. So it would indeed appear there is something not right if you are getting similar readings to what the manual says on my car.
 
So I finally busted out the second TPS I've got and checked some voltages - I got the same readings as the one that's currently on the EJ -> All backwards to what the manual (haynes) says it should be... I should check out one from the EA MPFI come to think of it - they may just be the same :D Things to do, things to do...

I really don't want to know the price of a new one but I would like it if someone else is able to back probe their TPS and see what voltage readings it gives at closed throttle and Wide Open Throttle (WOT).

Cheers

Bennie
 
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