On/Off Throttle Transition

[Rik]

My wife and I purchased our second Subaru last year – a 2003 Outback LTD wagon. I was a little hesitant because the last one we owned was back in the infamous Eighties when we had a GL-10 AWD Turbo sedan rust bucket. It was a nice car for the first couple of years, but after that things got bad.

 

Anyway, the new one seems very nice except for the on/off throttle transition. It’s very abrupt and I’m not sure if it’s due to the fuel injection system or a result of the flywheel. Either way, I hate it, especially when lifting off the throttle. It feels like your whole body is being thrown forward and it’s worse when you’re a passenger because you’re not expecting it.

 

Is there a fix?

[forester2002s]

What you are experiencing may be what others have called 'hesitation'. I also get this on my 2002 Forester, in first gear in slow traffic.

 

Try running a search on this board for the word 'hesitation'.

[rallyruss]

its not really a hesitation many subes new and old have this along with some other cars. It is caused by slop in the motor/trany mounts. I found that you either need to be verry gentle getting on and off the gas or try to find some stiffer mounts. I have also have expreimented with straping the tail of the trans. in place with old seat belt material. it actually worked well.

[Rik]

The condition I’m speaking of isn’t an engine hesitation. It can occur at any speed in any gear and only happens right at the point of transition from the injectors spraying or not.

 

Changing the mounts isn’t an option at this time. However, with all due respect, I really don’t think that’s the cause. And if it is, Subaru has a bad part supplier or they engineered a defective part.

 

Does anyone else have this condition and what have you done about it?

[Commuter]

Is this a manual or an automatic? (I'm guessing manual.)

 

I know that the Subaru's that I've driven have a more aggressive 'on' throttle response than is typical.

 

I don't know about 'off' throttle. Perfectly fine with my automatic (97 OB).

 

You might check into whether there was any ECU reflash recall for your car. There was some stuff going on a couple years ago regarding that, but I'm not sure of makes and models.

 

As suggested, it can be mitigated by altering your driving style a bit. I know... you shouldn't have to... etc etc. But, learning to 'ease' off the throttle instead of 'lift off' will become second nature if you do it for a while.

 

Perhaps a check of the throttle mechanism? I don't even know... what 'cushions' the throttle return these days? It's something I haven't messed with in years. Is it done electronically now?

 

Have you driven other 2003's to see if they are the same? That is, is yours typical, or distinctly different.

 

Commuter

[Rich in NEPA]

The condition I’m speaking of isn’t an engine hesitation. It can occur at any speed in any gear and only happens right at the point of transition from the injectors spraying or not.

I realize that it's often very difficult to describe a problem by what its symptoms feel like, so I offer this only as a possible explanation.

 

There was a thread on this forum a couple of months ago titled something like "A Crazy Problem" that sounded a lot like a strange problem I had with my previous MY2K OBW Ltd., H4 5MT, shortly after I bought it. What I experienced was a pronounced momentary delay or hesitation in engine response with an accompanying surge when going from off-throttle to mild acceleration, and when mildly decelerating to off-throttle there was a sudden lurch of deceleration. It occurred only when gradually increasing (or decreasing) pressure on the accelerator pedal right near the point of zero throttle (or when letting off on the pedal, even while moving at speed when coming to a stop or when the road grade goes slightly downward). The symptoms were noticeably worse on the highway with the cruise control engage!

 

The problem would come and go with no apparent rhyme or reason, sometimes even during a short or long drive. When it started acting up like this, it would usually last for a few days and then go away. Every once in a while the CEL would come on when starting the engine, with a corresponding error code for the throttle position sensor (TPS). The CEL would usually go out on its own (after 3 normal engine start/stop cycles if the fault clears the light should go out normally, but the code will be stored).

 

I checked the TPS myself on two separate occasions with a digital ohmmeter and it worked flawlessly. Finally after a couple of weeks, I took the vehicle to the dealer for service (just in case it actually needed a new TPS it would still be done under warranty) and all the mechanic did was pull apart the large square connector where the TPS leads go, reconnected it and the problem went away, never to return again. This plug may have come from the factory a little loose and/or a few of the pins inside became slightly oxidized, messing up the throttle response and causing the ECU to occasionally detect a bad TPS upon engine start.

 

On that particular H4 engine there were two large connectors about 1-inch square, one gray and one brown (one above the other), on the passenger side of and below the throttle body, mounted to a bracket on the engine itself. I can't recall which connector the TPS leads to. They're not hard to get at.

 

I can't say for sure if this is in any way the same problem that you're having, but if it sounds right to you then you could check for an intermittent TPS connection. It wouldn't hurt to try pulling the connectors apart, as well as the one on the TPS itself, and see if reseating them tightly a couple of times will cure the problem.

 

Either way, please do let us know what you find out.

 

Cheers ...

[Rik]

The car is a manual transmission 2.5 and you bring up a couple of good points. I’ll reseat the plug for the TPS and check the throttle mechanism.

 

I’d like to make it clear that I am not experiencing any surging due to the fuel delivery system when on steady throttle. And as with any manual transmission when going slow enough, sometimes there will be some bucking when idling down the driveway while in first gear, but that’s hardly unique to this car.

 

I guess what bugs me the most is the lifting off the throttle thing. If I’m traveling down the road at, say, 30 mph and I completely lift off the throttle to apply the brakes, the car decelerates more than I’ve experienced in countless other manual transmission cars I’ve had. In fact, it’s very motorcycle-like in that it feels like heavy engine-braking.

 

Maybe I’ll get some injector cleaner and run that through the system and see if that does anything. Does anyone know what the injector spray pattern is? Shower type with multiple holes or single pintle?

[Rich in NEPA]

I guess what bugs me the most is the lifting off the throttle thing. If I’m traveling down the road at, say, 30 mph and I completely lift off the throttle to apply the brakes, the car decelerates more than I’ve experienced in countless other manual transmission cars I’ve had. In fact, it’s very motorcycle-like in that it feels like heavy engine-braking.

This sounds uncannily like the TPS problem I had. It could be a bad TPS. Are the symptoms intermittent? Have you had the codes pulled, by any chance? (My understanding is that part of this sensor's function is to act like the accelerator pump on a carburetor, but I don't know how it fits it with deceleration and off-throttle response. Maybe someone else here can explain?)

 

Good luck with it.

 

Cheers ...

[Setright]

I have the same problem!

 

I haven't tried diagnosing it yet. I will say that some Redex Injector cleaner in the tank - which I do on the last tankfull before every oil change at 6k - seems to smooth things out a little.

 

Actually, when I had a free-flow muffler on, the symptoms were less pronounced.

 

For sure I am going to spray some contact cleaner on the connector terminals on the TPS. Top quality suggestion Rich!

[rallyruss]

with all due respect, I really don’t think that’s the cause. And if it is, Subaru has a bad part supplier or they engineered a defective part.

The mounts are verry soft to give you a nice vibration free feel when the car is running.

ALL subarus I have driven espically newer legacys have the drive train slop I am refering to. It fits your description perfectly. belive it or not thats how it is.

I used to modify VWs a lot and we would use stiffer rubber or urathane mounts to get rid of that nasty little lurch on and off throttle.

GM went so far as to add little shock absorbers on the motor to minimize this problem on thier cars.

yes a bad TPS or TPS circit can cause a similar problem but primarily on acceleration. A 2003 obdII car can pick up a bad TPS no problem. You would have a code set.

 

Rich- an ohm meter may not update fast enough to detect a TPS drop out. I use a high sample rate graphing meter. it has found TPS drop outs that my old Fluke meter missed.

[vic/se]

The car is a manual transmission 2.5 and you bring up a couple of good points. I’ll reseat the plug for the TPS and check the throttle mechanism.

 

I’d like to make it clear that I am not experiencing any surging due to the fuel delivery system when on steady throttle. And as with any manual transmission when going slow enough, sometimes there will be some bucking when idling down the driveway while in first gear, but that’s hardly unique to this car.

 

I guess what bugs me the most is the lifting off the throttle thing. If I’m traveling down the road at, say, 30 mph and I completely lift off the throttle to apply the brakes, the car decelerates more than I’ve experienced in countless other manual transmission cars I’ve had. In fact, it’s very motorcycle-like in that it feels like heavy engine-braking.

 

Maybe I’ll get some injector cleaner and run that through the system and see if that does anything. Does anyone know what the injector spray pattern is? Shower type with multiple holes or single pintle?

I believe the is more related to pressure plate and disc design, subaru wn,t admit it since it does it on many others like on mine ( a 2003 wagon m/t) so you have to adopte a diffrent driving method

[Rich in NEPA]

Keep in mind that, at least in my case (and it appears to be the same with RIK's situation), these symptoms are not subtle—they are quite pronounced and even unnerving, especially when following a slow driver! It was definitely not slop in the drivetrain, soft mounts, or even the usual "lurching" due to driveline backlash common to manual transmissions. Those conditions are there all the time and are usually an issue for drivers who are inexperienced with manual shifting. I've been driving MT's most of my adult life.

My understanding is that the OBD system only tests the health of the TPS circuit upon engine start up. I believe that's why I seldom got the CEL and why it would clear on its own. The circuit would "open" at some point during operation, perhaps due to rise in temperature or vibration. That's when the symptoms appeared. Other than this minor connector problem, my MY00 Outback Ltd. was absolutely trouble free for 43K miles.

Cheers ...

[Rik]

It sure sounds like you and I have had the same issue. And as far as I know (it’s really my wife’s car) the CEL has never come into play.

I haven’t had the chance to try the TPS connector thing yet, but I’ll get to it this weekend and see it that works. Stay tuned.

[Setright]

It was raining yesterday, and still is today, so I didn't feel like opening the connectors right up. I did re-seat them, and funnily it seemed to work for a while, but after a few separate runs the problem came back.

 

Once the weather dries up, I will dismantle and clean them properly. City life, with no garage sucks :-(

[rallyruss]

obd II system is always looking at TPS it uses the start up number as a base line to know what exact voltage closed throttle is. The problem is that it has a hard time determinting if a dorp out was caused by your foot or an open in the system. I am not saying you guys are crazy. I only wanted to point out that sube drive train slop is a bit of a problem. if you have another problem on top of that then yeah you really will be buckin and jerkin.

like I said the best test method is to use a high sample rate meter and sweep the TPS. if you do not have one find someone who does. I would help if you were local but of course its not the case. that is one of the only ways to catch a glitch like that.

 

good luck I understand it sucks to have a hyper senitive car.

[bmsmith]

I have a 97 Legacy GT auto and experience a similar problem to those described. I'm posting this mostly to just "get it out".

 

Maybe what I have is correctly called "hesitation", but I know exactly when it will happen though I don't understand why it happens. Hopefully my description makes some sense.

 

What I experience almost always happens after driving on the highway at high speed (60-80MPH) and then slowing down to a near stop at the end of an off ramp. At this point the ECU sometimes keeps the engine idling around 1000 rpm (according to my tach), which is high for my car. Maybe the ECU is in "performance mode"? If I stay at a standstill, the engine will gradually slow down to about 750 rpm, which is the normal idle speed for my car. But, as usually happens at off-ramps with yield signs, I end up slowly moving to the end of the ramp at 3-7 mph or so and never fully stop. During this period, as long as I keep moving, even slowly, when I touch the throttle I feel and see the engine rpm very briefly drop to below 500 rpm. It feels like the engine is about to stall. Then it catches and goes to 1200 rpm or so and I accelerate normally. It feels like a lurch. Letting off the throttle is usually fine, although sometimes I will feel a strange engine/transmission backpressure that gives a decellerating lurch type of feeling. The engine idles at 1000 rpm again and the same process repeats indefinitely throughout the ramp exit process. The only way to stop it is to completely stop the car and wait for the engine rpm to drop to 750, which takes 5-7 seconds.

 

I find it rather annoying, but I've never actually stalled, nor has it gotten any better or worse over time. It's always been this way since day one of owning the car, which I bought brand new.

 

- Brian

[CROSSBOLT]

Had the same problem with out 2003 Baja. Drove me nuts! Reset ECU by disconnecting the battery for half an hour the first time. Second time pulled the fuse on "Eng Ign" for 30 minutes. The trick after resetting the ECU is to drive and shift absolutely SMOOTHLY as possible for about 30 minutes in all gears with SMOOTH accel, transition and decel. This will work at diminishing this irritating transition lurch for a while. Whatever you do, DO NOT engage cruise control at any time during the driving after reset! The cruise sems to really install the lurch! Be prepared to reset the ECU about every 6 months. I think it is all caused by goofy programing and excessive backlash in the drive train. Subaru M/T is the only rig I have ever driven that has such a problem.

[Rik]

I’ve reseated the TPS connector as well as lubed and adjusted the slop out of the throttle cables (just because) and I’ve come to the conclusion that the condition the car has is inherent to the car. It’s just a sloppy driveline.

[Patrickjd9]

I took the Forester out of the running for our purchase for exactly this lurching. Haven't had it on our Legacy. We drove automatics in both cases, and I only felt it on the throttle, not off.

[CROSSBOLT]

I am sorry, Patrickjd9, that you de-selected the Forester. I thought our '01 was a great rig except for the rock hard seats and the downward kink in the cat back pipe. We had no noticable slop in the driveline with the auto trans. My real gripe is with the 5 speed MT in our Baja and the engine control programming that only allows for either torque out or torque in and no smooth transition. I think the slop is mostly in the ridiculous clutch. This will probably be my last Subaru because of these stupid problems and SOA attitude.