Wierd engine responce over 60mph when letting off gas

[gwoiler]

Some cars shut off fuel to the injectors when coasting and over a certain RPM. This Outback wagon with 2.5 seems to slow down too much when just slightly letting off the pedal at highway speeds. It is like you shut the key off!

And you can press on the gas a little and then some more and all of a sudden, you have power and are accelerating. Let off the gas just a little... not all the way, and then it is like the engine is breaking like as if you let fully of the pedal and had the ignition off.

Is this car supposed to do something like this? Is there a sensor somewhere that works with the TPS? It does not do it at lower speeds.

Also, when it does this, the Torque Converter is locked up and stays that way even when letting off the pedal a little and then it does this thing. This happens over 60 I think. Anyone understand what I am trying to say? This is a difficult one to describe. Oh... I just bought this car... it is a 1998 Suby Outback wagon with 112,000 miles. Other than this thing, it runs real nice.

Glenn

[deadlydave]

I know when I let off the gas on mine, it does slow down faster than anything I've driven previously.

How severe is this slow down? How many MPH do you loose in, say, 3 Seconds?

Welcome to the forum, Hope we can help. :smile:

[gwoiler]

I have done a search.... with inadequate words I am sure, but have read that many others have had this problem. One guy fixed it with messing with his TPS adjustment, but then it came back. the best way to describe it is drive straight and level at 70mph, and then without moving your throttle position.... just turn the key off. You would slow down at a faster rate then just taking your foot off the pedal in other cars. Some people from europe I think, described this as Lurching and jerking. Because.... the effect on the car from negative to possitive torque including the slop in the drive line was like a lurch forward or backwards. Go 70, turn the key off and on without moving the gas pedal and that is the best way to describe it! Lurch... or jerk! Something is wrong.

[Huffer]

How can you tell the torque convertor is locked up?

These cars do slow down dramatically if you let up on the throttle - sometimes there is a bit of forward/back pitching.

I like to use cruise... a lot.

[gwoiler]

Torque Converter..... OK. When the TC is not locked up, I can take my foot off the gas and see the RPM go down a few hundred... or step on it and watch it go up a few hundred. But at highway speeds when the TC is locked up, you can step on it or take your foot off the gas and there is no RPM change other than what would corrospond to changing vehical speeds.

[Huffer]

Torque Converter..... OK. When the TC is not locked up, I can take my foot off the gas and see the RPM go down a few hundred... or step on it and watch it go up a few hundred. But at highway speeds when the TC is locked up, you can step on it or take your foot off the gas and there is no RPM change other than what would corrospond to changing vehical speeds.

Does this depend on which gear you're in? Because if you're in any of the D modes, the tq convertor is always "locked up". ??

[gwoiler]

I have only noticed it in Drive on the dighway going fast. What is "D" mode? Is that just the D on the gear sellector?

[Huffer]

yep, D = D, D3, D2...

Anytime you have a D gear selected, the torque convertor is "locked up" because it's turning the wheels.

D = 90/10 torque split
D3 = 50/50 torque split
D2 = 50/50 split

Subaru 4EATs are mostly FWD drivetrains with a little rear push.

[gwoiler]

I think your wrong on that. If the TC was locked up all the time, you would not get very smooth driving / shifting! The TC has a certain amount of slip all the time unless it is locked up or 1:1. Some racing TC's slip as much as 2000 or 3000 rpm's.

A car slips 300-800 depending on the car. that is why your engine can idle in Drive while you are stopped and it does not stall the engine like if you let out on a clutch stopped. You can visually see the TC lock up when you get up to speed and with no shifts watch the rpm's go down about 300. At this point stepping a little on the gas or letting off does not affect the rpm as it does at slower speeds. Most cars WILL NOT lock the TC unless you are going over 45 mph.

I have 3 volvo wagons... one is a AWD and they are very similar to this. So are american cars.

If you are driving 50mph, straight and level... the TC isd locked. If you step on the gas... but not hard enough to make it down shift, you will see the rpm's go up because the TC unlocked. It is like a kind of over drive.

It was incorporated into most american cars when gas got expensive many years ago and then they added an overdrive.

But, seriously, the TC is not locked when you are in D unless you are going faster than 30 or 40mph. I will have to see what the actuall speed is on a Subary when it actuall will allow itself to lock up.

[Huffer]

Ok, I think I get what you're describing now.

Bottom line is, the TC isn't the problem - it's operating as it should.

[gwoiler]

Bottom line is I need HELP! :) There must be something telling the fuel injectors to shut down. I would not want this to happen unless I was removing my foot from the pedal... like a long downhill coast. So.... I am hoping someone on here will shed some light on this. thanks for your replys

[Huffer]

Some cars shut off fuel to the injectors when coasting and over a certain RPM. This Outback wagon with 2.5 seems to slow down too much when just slightly letting off the pedal at highway speeds. It is like you shut the key off!

And you can press on the gas a little and then some more and all of a sudden, you have power and are accelerating. Let off the gas just a little... not all the way, and then it is like the engine is breaking like as if you let fully of the pedal and had the ignition off.

Is this car supposed to do something like this? Is there a sensor somewhere that works with the TPS? It does not do it at lower speeds.


But that's what you said - is it minor pedal fluctuations or is it like the whole car shutting off? They're not nearly the same thing.

You will get some forward/back pitching when you lift-off throttle.

The injectors don't shut off - the engine is running.

[gwoiler]

Some cars shut off the fuel on down hill coasts when the engine is above a certain RPM. I don't know if Subaru does this or not, but I woulod bet my bottom dollar that the fuel is shutting off when I let off the gas pedal. I have read about other people having this trouble but I have not read the fix yet. You drive 70mph and then shut the key off and turn it on and do it again and that is what this would feel like. It is that drastic. A real jerk. Its not right. It is not the whole car shutting off. It is just way too much drag from letting just a tiny amount off the gas pedal. I am not even taking my foot all the way off the pedal... just letting up a 1/4 inch.... just enough that I would start to slow down.... slowly! Not a massive deacceleration.

[dodik]

yes cars do shut off fuel but only when speed exceeds allowable rpms per certain gear meaning it will cut fuel if you go more than allowed and your rpms would be at redline. something tells me you should check your fuel system like filter for example if thats good check the pump and injectors

[Sarra]

The TCU controls TC lockup; it'll only lock the TC up in 4th gear, when you're cruising steadily.

When you're in gear and not on the gas, the engine will cut fuel, and IIRC, it won't start fueling again until around 1,500 rpm. When you're engine braking, there's really no need for fuel... It's not necessary to keeping the motor running, so the ECU stops your injectors temporarily.

I'm glad you all think that the 4EAT's off throttle engine braking is awesome, because I sure don't. My mom's 2003 Outback sucks, you let off the gas and it just drifts IMO.

dodik, that's a different kind of fuel cut, that's the rev limiter. The fuel cutoff mentioned was engine braking, not engine breaking.

gwoiler, is there perhaps a problem with your throttle cable? Sounds like it might have a little too much slack. Poke it a bit, and if it isn't the cable, then at least you can rule it out.

[Reason]

What you are experience isn't normal. You shouldn't have such a jerk when letting off the gas. I notice quicker deceleration when I took my foot off the pedal when I got a lighten crank pulley but still wasn't that bad.

As for the fuel cut off what are you guys talking about? No matter what there has to be some fuel flowing to keep the motor running. 1500 rpm's or less theres a fuel cut?? Maybe I misunderstand you Sara but that doesn't sound right. Maybe 3 out of the 4 injectors?

[MCarp22]

No matter what there has to be some fuel flowing to keep the motor running.

The force of the road spins the transaxle spins the crankshaft. No fuel required.

[Reason]

No matter what there has to be some fuel flowing to keep the motor running.

The force of the road spins the transaxle spins the crankshaft. No fuel required.

I'm thinking more at idle. I was taking a hit at the 1500 rpm or less comment.

[gwoiler]

I'll check to see if there is any slack in the throttle cable. I guess from all the comments that I am not describing this right.

When going down a hill, and you let off the gas, it is the transmission that turns the engine... Throttle possition just determines how much breaking there will be. Less throttle more breaking. Shut the fuel to the injectors and it is maximum engine breaking. The engine still turns and for most people, they won't kow that they are burning no fuel. But if the system does not coordinate it properly it will be rough... as in my case. So I am looking for someone that can point me to trouble shoot this. So far only one reply has said anything intelligable. -- The TCU I am guessing is a torque Converter control unit???

That is waht I need, is some knowlegable info to fix this... not a lot of ideas. No critisism intended here, but I need to figure this out.

If your cruising at 70mph and your foot is 1/3 down on the gas pedal, and you let up an 1/8 inch..... it should slow that much.... not engine break as if you turned the key off. And then press down that amount... 1/8 inch and bamm.... your accelerating. Under 50 or 60 it is normal... nice and smoothly transitioning between breaking or accelerating.

[Huffer]

I'm going to recommend you find a decent Subaru service department in your area, and go for a ride with the service manager or an experienced tech.

If you can demonstrate the problem, that will be better than trying to describe it multiple times on a forum.

[gwoiler]

Your right! And cost my wallet more than fixing it myself too! One place to start looking troubleshooting would be nice! Hope I did not offend anyone here.

[Huffer]

I didn't say you had to have the dealer fix it - all I'm saying is that it might be something that is actually normal, relative to the car you're driving.

See if you can take another car thats the same year/model for a testdrive and if it does the same thing...

:shrug:

[gwoiler]

We have the same exact car but in a 96 instead of a 98. A search has turned up on other forums people experiencing this same thing. One guy temporarily fixed it by messing with his TPS. I guess no one in here has been succesful at fixing this. I'll find another forum. Thanks for your time.

[Huffer]

I'm thinking no-one here has experienced the problem.

I've got 2 late-90s Subaru's, and have not experienced the problem you keep talking about.

Do you have a link to the "other guy" that messed with his TPS?
Perhaps all you need is a new TPS?

[Reason]

I'm thinking no-one here has experienced the problem.

I've got 2 late-90s Subaru's, and have not experienced the problem you keep talking about.

Do you have a link to the "other guy" that messed with his TPS?
Perhaps all you need is a new TPS?

I was thinking the same thing. I never experienced it or heard of anything like it.

[Wiscon_Mark]

It's called Aerodynamics.

[deadlydave]

I know when I let off the gas on mine, it does slow down faster than anything I've driven previously.

How severe is this slow down? How many MPH do you loose in, say, 3 Seconds?

Welcome to the forum, Hope we can help. :smile:

Perhaps in the heat of the moment, we overlooked the 2 questions I posted early on. The question's been danced around --we have 'feelings' and what it's 'like', but no hard numbers to compare. I know the slow down is pretty pronounced in my Legacy, but AWD is heavy and friction-laden--I always attributed the slow down to the AWD and the air resistance at highway speeds.

How severe is this slow down? How many MPH do you loose in, say, 3 Seconds? 5 Seconds? 10?

[Huffer]

As a quick comparo, when I'm crusing @ 65mph in 5th, and I let off the throttle, on a calm day I slow to 60mph in roughly 5-7seconds. This is in the wagon, which is supposed to be more aerodynamic in a straight line than a sedan.

[deadlydave]

As a quick comparo, when I'm crusing @ 65mph in 5th, and I let off the throttle, on a calm day I slow to 60mph in roughly 5-7seconds. This is in the wagon, which is supposed to be more aerodynamic in a straight line than a sedan.
Sweet, good to know. Anyone with an auto wanna chime in? I really wanna do this myself to find out, but the stupid wheel bearing/Half-shaft PITA makes me fearful to drive.

[Sarra]

I'll check to see if there is any slack in the throttle cable. I guess from all the comments that I am not describing this right.

When going down a hill, and you let off the gas, it is the transmission that turns the engine... Throttle possition just determines how much breaking there will be. Less throttle more breaking. Shut the fuel to the injectors and it is maximum engine breaking. The engine still turns and for most people, they won't kow that they are burning no fuel. But if the system does not coordinate it properly it will be rough... as in my case. So I am looking for someone that can point me to trouble shoot this. So far only one reply has said anything intelligable. -- The TCU I am guessing is a torque Converter control unit???

That is waht I need, is some knowlegable info to fix this... not a lot of ideas. No critisism intended here, but I need to figure this out.

If your cruising at 70mph and your foot is 1/3 down on the gas pedal, and you let up an 1/8 inch..... it should slow that much.... not engine break as if you turned the key off. And then press down that amount... 1/8 inch and bamm.... your accelerating. Under 50 or 60 it is normal... nice and smoothly transitioning between breaking or accelerating.

TCU is the Transmission Control Unit, it's the E in 4EAT. The TCU controls the torque converter lockup, which gear you are in, and how the transmission shifts.

I can think of several things that would cause something like this. Bad plugs, bad wires, a bad coil pack, a vacuum leak or bad vacuum hose(s), injector problems, clogged fuel filter, bad air filter, really old ATF, possibly a bad engine or transmission mount, worn/damaged/misaligned center diff, etc.

If the car is slowing down faster than it should under engine braking, then I would suspect it is a transmission problem.


As for the fuel cut off what are you guys talking about? No matter what there has to be some fuel flowing to keep the motor running. 1500 rpm's or less theres a fuel cut?? Maybe I misunderstand you Sara but that doesn't sound right. Maybe 3 out of the 4 injectors?

If you're going 100 mph, maxed out in 4th gear (5 speed), and you take your foot off the gas, don't touch the brake, and leave it in gear, foot off the clutch, you will be slowing down. Stomp the clutch, and you'll slow down at a reduced rate (slowing down slower). This is engine braking, when the throttle is closed. Whent he throttle is closed, all the air going into your motor, except for some through your idle bypass, is blocked. The cylinders will keep moving side to side, your valves will keep opening and closing, but the only think keeping your engine turning will be the flywheel, via the clutch, gearbox, axles, and your tires. Basically, you turn an air pump, your engine, into an air brake. Each time the intake valve opens, as the cylinder moves down in the bore, it's creating a vacuum in the combustion chamber. Since the throttle plate is closed, there's more vacuum than when the throttle is open, even partially, which causes the piston to resist moving all the way down the bore. Burning fuel would be useless, a complete waste of fuel, so the ECU will just shut off the injectors. Since the pistons have to keep sucking in air as the car is moving, it causes a braking action on your tires, just as if you were lightly pressing on your brakes. It'll keep the injectors off until you hit around 1500 rpm, when it will start fueling again, and eventually, open the idle bypass enough to maintain idle.

When you hit your rev limiter, it just cuts off the fuel for a moment, but the throttle is open. Doing so with a wet nitrous kit can cause danger to manifold.

[ProdriveDreams]

While the lower presure air entering the cylinder does slow the car some, more importantly the cylinder is then compressing that air but since there is little air and little to no fuel (not sure on the fuel cutoff thing) there is very little powergain, so the engine is using more power compressing and moving the air then it is gaining from the minute amount of burnt fuel.

Additionally part of the reason subaru's slow down much more when you coast then most other vehicles is that even when you are in neutral and coasting all the CV joints, hubs, driveshafts, and the output shaft must be spinning, thats a LOT of additional rotational weight and resistance versus a two wheel drive car. This shouldnt cause a lurching though.

just a few thoughts to add.