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Discussion Starter #1
So my '01 OB limited started giving me trouble a few weeks ago. It would seem to lose power when taking off from a stop. Sometimes it would "buck" a few times till up to speed (over 30 mph lets say). Idle was also very rough. I pulled the IAC solenoid and cleaned what looked like oil build up. Driving home after that it ran SOOO much better....for about 4 mi. :mad: It started bucking again with the rough idle at a stop.
Now, here is the best part. The next whole week driving back and forth to work (about 8 mi each way) the car runs great, like nothing ever happened. :confused: Then 1 day it all comes back. Only for a day or so. Last monday I leave for work and hardly make it off my street! Rough idle, bucking when I give gas, and NO power. Had to park it and take the mini van.
PCV valve, fuel filter, fuel pressure regulator have all been changed. What next? Vac leak? Fuel?
No CEL light either! I almost wish it would;).
Any thoughts would help, thanks.

Nathan
 

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Just because there is no light doesn't mean there aren't pending codes.

A pending code is a note made by the computer when it thought it saw something... but nahh, wasn't conclusive enough to turn on the warning light. But it makes a note for next time, so that several intermittent faults can be evaluated together.

It's worth connecting a scanner (or driving to a shop that does free scans) to see if there are any pending codes logged.

Are there any other factors related? Temperature/humidity? hot start/cold start?

What led you to changing the fuel pressure regulator? Any chance the pump itself has gone intermittent on you?
 

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Could also be the front o2 sensor, it controls the air/fuel ratio. If it is still the original it might be good to change it anyway, it could however be on its way out too. I had the same symptoms when it was failing on my 2006 Subaru Forester.
 

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it's worth pointing out that the onboard diagnostics don't have a pressure sensor to help pinpoint a fuel pump failure. So if the pump is failing, there is no specific error code for that.

Obviously, lack of fuel can make the engine run funky and cause symptoms related to other trouble codes, which is can be very confusing.
 

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Discussion Starter #8
No codes pending. Checked again this morning with Torque on my Droid 4.

Changed fuel pres reg thinking it could be causing problem without codes.

Wires and plugs are about 15,000 mi old. I think I changed them the same time as I did head gaskets.

Performance Suby, did your forester throw codes when O2 sensor was failing?
As far as I know it's original but at $150 from dealer I am hesitant to change.

Fuel pump sounds suspect but no strange noise (ping) when trying to accelerate. Not when power loss starts or when running fine.
 

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Discussion Starter #9
Does front O2 really need to be from dealer? Rock auto wants only $45 for upstream Bosch sensor. Has anyone had experience with similar sensors?
 

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No codes pending. Checked again this morning with Torque on my Droid 4.

Changed fuel pres reg thinking it could be causing problem without codes.

Wires and plugs are about 15,000 mi old. I think I changed them the same time as I did head gaskets.

Performance Suby, did your forester throw codes when O2 sensor was failing?
As far as I know it's original but at $150 from dealer I am hesitant to change.

Fuel pump sounds suspect but no strange noise (ping) when trying to accelerate. Not when power loss starts or when running fine.
It could be running bad due to too much fuel which could again be related to misinformation from the TPS, MAF, AF sensor, slow CKP or CMP, or stuck injector.

If its not pinging, its not leaning out. So that narrows it down to "flooding" the cylinder due to data from one of the sensors, timing is off for acceleration due to one of the above sensors, misfiring due to coil malfunction, or electrical conductance is low.

In order to find the problem, you need to either be able to read the live data yourself and know what it is showing you, or take it to a shop that knows what they are doing.

The AF sensor should be steady at 3.2v at idle. The Map should show a relative pressure between 6-8 depending on the current BARO pressure. TPS can be checked with the key on, engine off by watching the % open from closed to WOT. If it gives you a voltage reading instead of percentage, WOT is about 4.5v. MAF, if your engine uses one, should read approx 3.2-3.7 gps.

Bad grounds will make a car run stupid. Period. Check all the ground anchors and any suspected ones, clean them. There are a lot. There is one set on the intake manifold that grounds the AF, O2, TPS and IAC. If its corroded or loose, it will effect the performance of these sensors and the engine. I've had some 2.2 and 2.5 come in with corroded grounds that would make the car shut off like you turned the key off and not start up. Cleaned the grounds and viola, start up and everyting worked again.
 

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When I first started having issues with rough idle, hesitation and lack of power I did not have a CE light on the Forester. At the time I figured I had bad gas, but as time progressed it got worse to the point where it stalled or almost stalled every time I stopped to idle at this point the CE light came on and it came up as the front o2 sensor, which I replaced with a Denso replacement from RockAuto.

This is part of the reason why I am going to replace it in my Outback now because it is the original, and I am having some problems some vibrating at idle (even though it idles at around 750 rpm) and a slight lack of power. I have already replaced spark plugs, wires, timing belt, pulleys & tensioner, fuel filter, pcv valve, cleaned iacv.
 

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Discussion Starter #14
I have not tried the spray bottle trick yet, would that help narrow down a bad ground? Worth a shot anyway right.
My dad knows a guy who has a nice scanner. I think I'll try to get some live data on a few sensors before I start buying parts again.

Thanks again to all that have replied. I will keep you posted.

Nathan
 

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Definitely try to figure it out instead of blindly replacing parts... there are a lot of parts.

The spray bottle trick is specifically to test ignition wires, nothing else.

Bad grounds can't (usually) be seen and are hard to measure. Best way to deal with them is to find the grounding points, disconnect the wires, clean everything that makes contact and put them back together. Re-read Cardoc's post #10 for further detail.
 

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The spray bottle trick is specifically to test ignition wires, nothing else.
Yup, and it wouldn't take too long or hurt test the wires, since...
Wires and plugs are about 15,000 mi old. I think I changed them the same time as I did head gaskets.
I could be mistaken [wouldn't be the first time] but I thought that test could tell you somersetting about the integrity of the coil as well. I had similar symptoms, though not as severe, before I changed my coil. When faced with a problem my diagnostic technique is to find advice like that offered here, make a list and test the advice.
 

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Yup, and it wouldn't take too long or hurt test the wires, since...
I could be mistaken [wouldn't be the first time] but I thought that test could tell you somersetting about the integrity of the coil as well. I had similar symptoms, though not as severe, before I changed my coil. When faced with a problem my diagnostic technique is to find advice like that offered here, make a list and test the advice.
Well put. :29:

Check, check and check again before wasting time and cash on parts.

It may seem like a chore, but some of the electronics on Subie's are not cheap. Just and example, IAC on the older 2.5 was electromagnetic and was controlled by the ECT signal to the ECM. They never failed, but one time an owner thought to remove it, I forget why, and damaged the pintle causing it to bind. Then it was about $450.00 USD for the part.
 

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I had a bad ground once. I missed getting it tightened after replacing the head gaskets. The car ran horrible, shifted like a drunk, and gauges and warning lights were all freaking out. It had me freaking out! Finally found the ground because I heard it buzzing and arcing with the key on. Not sure that's the problem, just saying that bad grounds will do crazy things.
 

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Discussion Starter #19
So I pulled and cleaned the battery last weekend. It had some corrosion around the bracket but nothing to crazy. I removed 2 other ground wires close by, including the ground for the intake and brushed the bolts and ends. Seems to be running fine again this week :)
I did find a ground on the right side shock mount that wasn't bolted down. Must have been like this since the HG job (2yrs ago). Does anyone know where this might go? Another ground for intake?
sorry, having trouble uploading pics
 
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