Partial throttle cut-out

[destey]

1997 Legacy GT w/2.5. Here it is: Car drives ok at full throttle and 2/3, but if you go under that, its like someone turns the key off. It loses complete power. If you let off the throttle all the way and then come back on, the engine runs fine. If you push it further down, at some point the motor come back on like a light switch with a slam as all the power comes right back.

 

It is the worst when I'm driving along at low load on level ground. All it does is die and surge back to life constantly.

 

I've done the following:

 

plug wires

TPS

o2 sensors

MAF sensor

knock sensor

IAC rotates freely

 

I don't know what else it could be. It has check engine light was read as misfire.

[94Loyale]

Sounds like spark plugs to me. I'd change them out.

[Rooster2]

I am thinking bad gas, maybe got some water mixed in with the gas. Suggest you add a bottle of "dry gas," to the gas tank to see if that helps.

[Suba9792]

vacuum leak?? is it an AT or 5MT? check the EGR. sounds like a vacuum leak to me or failing fuel pump.

[destey]

Its a 5mt with an EGR. The EGR feels like it operates ok when I move it by hand, no binding or anything. Put in some new plugs and dry gas but it didn't help, I don't see any vacuum leaks though maybe I'm not seeing it. This one has me stumped

[Rooster2]

fuel filter and or failing fuel pump?? You have addressed most everything electrical.

[destey]

fuel filter is about 2 years old I think. Would a bad fuel pump be worse at higher rpm? Mine seems bad at low throttle. I'm going to revisit the IAC, maybe its binding after I put the motor housing back on.

 

Could it be a crank angle sensor or cam sensor, partially clogged injectors, bad ECU or maybe failed fuel pressure regulator?

[Rooster2]

fuel filter is about 2 years old I think. Would a bad fuel pump be worse at higher rpm? Mine seems bad at low throttle. I'm going to revisit the IAC, maybe its binding after I put the motor housing back on.

 

Could it be a crank angle sensor or cam sensor, partially clogged injectors, bad ECU or maybe failed fuel pressure regulator?

 

I have always associated a bad fuel pump with an inability to provide gas at high rpm, so maybe your fuel pump is okay.

 

Does pulling the code(s) yield any more information then just "misfire?"

[davebugs]

I have always associated a bad fuel pump with an inability to provide gas at high rpm, so maybe your fuel pump is okay.

 

Does pulling the code(s) yield any more information then just "misfire?"

 

 

It should tell you what cylinders are miss fireing.

 

I've experienced similar symptoms on early 90's with bad fuel injectors. I forget if the red ones or grey ones were the "better" ones. Haven't had trouble with the 95-99's but symptoms sound alike from what I remember.

[destey]

The missfire code was just what the previous owner said, bought the car a few weeks ago with a discount because it didn't run right. I'll go have the codes read. If it is an injector it might tell me which one. Is there any way to clean up the injector if its clogged?

[Rooster2]

I have always used a high quality injector cleaner additive to the gas tank. Chevron Techron is very good, as well as one sold by Lucas Oil. The good cleaner additives cost $6 to $7/bottle. Avoid the cheaper cleaners that sell for less. They are mostly just alcohol, and don't work well.

 

I keep thinking about how your motor is misbehaving, and can't help but think that it must be something simple, and prolly inexpensive to fix the problem. Otherwise, the motor would not rev up and run well and strong at high rpm. I hope pulling the codes tells you exactly what is wrong. PO saying the problem is misfire, may or may not be accurate. You have no way of knowing if he was telling you the truth. Yea, it could be the injectors, but maybe something simple like a sensor. But, I see that you replaced possible problem sensors.

[Manarius]

Sounds like a failing Mass Airflow Sensor to me. When that sensor fails, the car can have all kinds of weird behavior; poor throttle response included.

[Rooster2]

Sounds like a failing Mass Airflow Sensor to me. When that sensor fails, the car can have all kinds of weird behavior; poor throttle response included.

 

You can pick up a used Mass Airflow Sensor at a wrecking yard on the cheap. Pulling the codes, may even tell you that this sensor is bad.

[destey]

I swapped MAF with another vehicle, runs the same. I'll give the injector cleaner a try. I'll try and get the code read. I'm at a different place than I normally am for work this week and the autozone that reads codes isn't nearby, so it might be until next week.

 

Someone at work also said that the TPS has to be set by a multimeter and maybe the guy before me messed it up and when I swapped one in I didn't install it properly.

[Rooster2]

I swapped MAF with another vehicle, runs the same. I'll give the injector cleaner a try. I'll try and get the code read. I'm at a different place than I normally am for work this week and the autozone that reads codes isn't nearby, so it might be until next week.

 

Someone at work also said that the TPS has to be set by a multimeter and maybe the guy before me messed it up and when I swapped one in I didn't install it properly.

 

Injector cleaner takes maybe 25 miles of driving before any noticeable improvement is felt. With your "bucking bronco" Subie that may be the worst 25 miles of driving in your life. Gotta think your problem won't be solved with injector cleaner, but it can't hurt.

[destey]

I had been driving the car but I started it yesterday and it was all of the sudden undriveable. It runs extremely rough and the accelerator peddle is barely responsive. It sputters sometimes I can get it to rev where after about 2500rpms it cleans up and I can rev it up to redline. The check engine light flashes on and off with the engine RPM, the faster the engine spins the faster the flashes. There's an audible click like a solenoid every time the CEL flashes. Once I get over 2500rpm the clicking stops and the CEL stays constant at the same time it smooths out. I don't know about power because as I take it down my driveway all it does is buck and quit unless I really rev it up.

 

I've unpluged the MAF, no change, car doesn't run rougher, doesn't run smoother. Same with the TPS, IAC, knock etc. Its as if the ECU is ignoring every imput and running in some limp mode. Whenever I've unplugged the MAF on this car before now or any other subaru it runs noticeable rougher or dies immediately.

 

Since then I've tried the following

 

another new set of plug wires

different coil

MAF

TPS

 

checked all fuses. Its got a strong battery in it, plugs I just changed. I'm at a loss, anyone have any ideas?

[Manarius]

I had been driving the car but I started it yesterday and it was all of the sudden undriveable. It runs extremely rough and the accelerator peddle is barely responsive. It sputters sometimes I can get it to rev where after about 2500rpms it cleans up and I can rev it up to redline. The check engine light flashes on and off with the engine RPM, the faster the engine spins the faster the flashes. There's an audible click like a solenoid every time the CEL flashes. Once I get over 2500rpm the clicking stops and the CEL stays constant at the same time it smooths out. I don't know about power because as I take it down my driveway all it does is buck and quit unless I really rev it up.

 

I've unpluged the MAF, no change, car doesn't run rougher, doesn't run smoother. Same with the TPS, IAC, knock etc. Its as if the ECU is ignoring every imput and running in some limp mode. Whenever I've unplugged the MAF on this car before now or any other subaru it runs noticeable rougher or dies immediately.

 

Since then I've tried the following

 

another new set of plug wires

different coil

MAF

TPS

 

checked all fuses. Its got a strong battery in it, plugs I just changed. I'm at a loss, anyone have any ideas?

What kind of car?

 

Did swap MAF's with someone? Did you check the CEL code? Can you narrow it down to a certain cylinder by unplugging the injectors one-by-one and seeing if the car runs rougher on a certain one? Did you check the O2 sensor?

[destey]

Its a 1997 Legacy GT with 2.5. I had the codes read and it said p0420 cat system efficiency below threshold.

 

I made a video of what its currently doing. This wasn't the best morning to take the video as it got down to -20F. When its not as cold it starts and I can get it to rev by pumping the throttle. The CEL stops clicking and stays solid at the same time it smooths out at about 2500rpm.

 

http://s1227.photobucket.com/albums/ee421/qqqqqwwww/?action=view&current=SDC11236.mp4

[Setright]

The po420 code is probably a result of the problem, and not the cause. Raw fuel or too much air is making the 02 sensors go bannas.

 

But why?

 

 

It's hard to find a theory consistent with lousy low-rev running, but smooth high rev performance.

 

Fuel pressure regulator? Usually would give the opposite symptoms, but let's say the pressure is TOO HIGH....so the engine runs rich at low revs.

 

Any chance you can swap the FPR?

[destey]

fuel pressure regulator would cause these syptoms but the CEL flashing makes me think its electrical of some sort. Maybe its the alternator? I recently brought the battery in because of the cold and charged it, so maybe a bad alternator has been hidden by that. I noticed the headlights dim noticeably as the CEL flashes. Could it be wire rub through, crack or melting?

[The Scooby]

fuel injector cleaner will do nothing for you if the injectors are clogged or restricted. its more of something you use all the time to maintain them. if they are clogged you need to pull them and have them professionally cleaned and flow tested.

 

if its throwing a po420 that cat is bad. could be breaking apart and clogging the exhaust.

 

i recomend you take the car to a shop that knows what they are doing. i would hook up a scanner and read the pids to see what everything is doing at idle and while driving.

[logic23]

your engine seems to be waaaay to rich. you have to rev it to clear the excess fuel...this is tripping the p420. It could be the temp sensor (2 wire one) , a bad fuel injector, throttle position sensor... i would go after the sensors on the manifold. If there is a donor car take the whole manifold off and put it on your car. it takes about 30-40 min to do the swap the first time. The egr metal pipe is sometimes hard to get broken loose. You'll also need intake gaskets. When I have cars come in the shop with these symptoms the whols manifold swap is the fastest/cheapest way to narrow the issue. If it still runs poorly then you've eliminated a lot of variables in one shot.

[destey]

the clicking is coming from the relay or whatever that green plug goes into under the dash. What does it do?

 

I circled the part making the clicking.

 

[Setright]

You don't have the green, single wire connectors under the dash connected do you? Normal "position" is disconnected.

[destey]

You don't have the green, single wire connectors under the dash connected do you? Normal "position" is disconnected.

 

I remember seeing them disconnected.

 

I replaced the relay that was making the clicking, it still makes the clicking. I also swapped out all the relays I could find with my parts car, if the relays were the same (9/10 were) It feels like its running on 3 cylinders but I could be wrong. I unplugged the injectors one at a time, the drivers side rear cylinder didn't seem to make it run any worse when I unplugged it. But its running so rough its hard to tell.

 

I was going to swap injector rails over from the 1995 legacy parts car but I looked up the injectors and the part numbers are different. Looks like 95-96 is different from 97-99. If I swapped them over as a set of 4 would that make it ok?