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2004 H6 Outback Wagon "35th Anniversary Edition" w/o front bumper
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Discussion Starter #1
I took my 2004 Outback on a pretty small trip, 39 miles, but it was over some fairly elevated ridges. I think the highest one peaks at 3,000 ft. Still, up that incline, the old beast was pushing 4-5k RPM to keep at 75 MPH.

When I got back into town an exited the freeway, I came to a stop-light at the end of the exit. I noticed a low idle, only 350 RPM according to Torque. I pressed the gas a little because I didn't want it to stall, revved it up above 2k RPM, and then just dropped the accelerator and when the RPM plummeted down, it dropped well below 300 RPM and the engine stalled.

It started right back up, and I haven't had this issue again with just simple in town driving. I'm suspecting the PCV valve since I've needed to replace it for a long time, and sometimes I have unexpected surging during driving. But I'm not sure it can cause stalling like this?
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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Did you have to jump the car to start it? Or have a battery replacement done right before this trip?

Sounds like a "first start" without the idle relearn procedure done.

Could also be a gummed-up throttle body and the throttle plate is getting stuck.
 

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OBW H6 VDC, Tribeca, XT6
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Idle air control valve.

They typically are problematic when you first start idling - after coming to a stop, letting off the gas, etc. Car will stall. They get dirty or old and aren't properly allocating air flow when the throttle plate closes.

I'm not sure how to test/verify, I'd just swap in a used one but I've got them on hand.
You can often clean them, though I've never had to on a 3.0.

Read OBDII codes and post what you got here.
Are the spark plugs 15 years old?
 

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2002 3.0 VDC Wag + 2018 2.5 Leg Ltd
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if you pull the IACV apart to clean it, have a gasket in your hand, (a square frame made out of rubber),

$5 for OEM or aftermarket.
old one may not get back in place after 15 years.
 
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2004 H6 Outback Wagon "35th Anniversary Edition" w/o front bumper
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Discussion Starter #5
Dang, I have had the IACV on my to-do list for a while. Last time I got all ready to do it, I took apart my throttle-body and it looked nothing like the pics I'd found to guide me through, and someone had convinced me that it probably wasn't bad, so I returned the parts and forgot about it. The reason I suspected it is because when I start the car in the colder months, it starts at a high idle of like 1200 RPM, and then kind of ebbs up and down steadily over a few minutes until it settles out at about 700 rpm, but at times will seem like it wants to run at a lower 650ish rpm in traffic after it's been moving around. I track it with Torque, but just didn't have the proper log settings when I went on this trip to have better data for what was happening with the engine.

There's a chance the dealership put fresh plugs in since I bought it from them used at 93k, but I wouldn't put it past them to have just kept the old ones in there given that they're "long life". The engine has 140k on it now.

Nothing's been done with the battery or anything like that since last winter when I replaced the battery and the cable from the starter. I don't get any codes from an OBDII scan, and while in town it seems to run pretty smooth, it was just over that short trip with the inclinations and cold air that taxed the engine that I started seeing problems.

I have this kind of gut-feeling that it's the cold air that is taxing it over the inclines. It doesn't struggle for power the same when it's warmer out, and I don't think it's related to when they switch to winter-gas mixes because I track my fuel economy with Torque Pro and can watch it dip pretty steadily as the temperatures drop from late-summer into early-fall. Meanwhile, these ridges are not extremely high altitude, but it's a desert environment so they do get very cold, and within a pretty short ascent. It's literally like driving into a frozen zone when you were just in the sunshine, and whenever it's in these frostier inclined portions, the engine has to get up to 4-5k RPM to keep it at 70-75 MPH, and often times will drop into 3rd and surge up into the 5500-6000k range for a short bit before shifting back into 4th.

Not sure how that could relate to the IACV, but I got over the last one of such ridges and drove another 10 miles or so before coming to a stop at that particular stop-light. In my mind I don't think that's a real significant distance or amount of time to say it's not unrelated to the power struggles it was having over the inclines?
 

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03 H6 OBW & 06 WRX Sportwagon
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bad knock sensors and bad engine temp sensors can occasionally be bad without throwing codes. they can kill power under certain circumstances.

vacuum testing is cheap/easy and can sometimes find issues. compare readings cold vs hot ?

look on-line for a list of problems it can detect.
 

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I would hope things that are bad enough to stall a car would make for a code.

expensive would be a trans problem.

__

in post 1 you mentioned a PCV. I wonder if wildly out of wack if one could stall a car. vs just making it miss or buck.

$14 buys a new OEM.

11810AA021

https://www.amazon.com/Subaru-11810-AA021-PCV-Valve/dp/B00L2OF3N2/

sometimes the piping on those gets brittle. (winter time makes such things even more brittle / hard to deal with too).
 

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2004 H6 Outback Wagon "35th Anniversary Edition" w/o front bumper
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Discussion Starter #8
I would hope things that are bad enough to stall a car would make for a code.

expensive would be a trans problem.

__

in post 1 you mentioned a PCV. I wonder if wildly out of wack if one could stall a car. vs just making it miss or buck.

$14 buys a new OEM.

11810AA021

https://www.amazon.com/Subaru-11810-AA021-PCV-Valve/dp/B00L2OF3N2/

sometimes the piping on those gets brittle. (winter time makes such things even more brittle / hard to deal with too).
Don't say that! Sometimes it feels like it's shifting kinda hard, but I've heard that these 4-AT transmissions aren't really that smooth to begin with. The dealership wants $93 just for a diagnostic though.

I've been meaning to replace the PCV just because I know it's old.

1 Lucky Texan,

Do you mean a list of problems Troque can detect? My big problem is I thought I had been logging more data than I have been so I have no real hot readings to judge cold ones from :/

Edit:

The one and only code I've ever had for this car was one relating to fuel. I can't for the life of me remember the code, but I remember it happened in the cold and on the highway as well, and after I changed my fuel filter and cleared the code, I never got that one again. I'm trying to look through my old posts to find the code, but it sputtered quite similarly that day, but that time was different because it was all over flat ground.
 

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2004 H6 Outback Wagon "35th Anniversary Edition" w/o front bumper
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Discussion Starter #9
Well, an interesting development, I got a P0420 code. I checked out some stuff on TorquePro, and it seems like maybe it has something to do with the rich:lean ratio? I also took a look at my O2 sensor on a live reading, it would just get this little dip every now and then. I've been running with full logging available if there's any readings I should put up to help diagnose.
 

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On the Super Mod Squad
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Well, an interesting development, I got a P0420 code. I checked out some stuff on TorquePro, and it seems like maybe it has something to do with the rich:lean ratio? I also took a look at my O2 sensor on a live reading, it would just get this little dip every now and then. I've been running with full logging available if there's any readings I should put up to help diagnose.

p0420 is a nag code. created by something else with other codes, or a rear o2 sensor getting old and dirty. does nothing for or how the car runs.

forget about it until something else crops up.
 
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2004 H6 Outback Wagon "35th Anniversary Edition" w/o front bumper
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Discussion Starter #11
p0420 is a nag code. created by something else with other codes, or a rear o2 sensor getting old and dirty. does nothing for or how the car runs.

forget about it until something else crops up.
Yeah I kinda got that feeling reading about it. Anything to the rich to lean warning? That's not really an engine code but a test Torque does.
 

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Yeah I kinda got that feeling reading about it. Anything to the rich to lean warning? That's not really an engine code but a test Torque does.
keep trying, it might pop some code in reference to a front sensor soon.
 

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2004 35th Aniversey Addition Outback ,2018 2.5I limited Outback
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I had a similar problem with my 2004 H6 and it turned out to be the throttle position sensor.
 

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2004 H6 Outback Wagon "35th Anniversary Edition" w/o front bumper
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Discussion Starter #14
keep trying, it might pop some code in reference to a front sensor soon.
I had a similar problem with my 2004 H6 and it turned out to be the throttle position sensor.
Today on my way home the car began "surging"... It would accelerate quickly, then kind of pause, felt like someone was lightly hitting the break every once in a while. Then it started getting REALLY bad, and the engine went from pulling 2200 RPM to stay at 60, to 3200 RPM, and then finally I got an engine code P0122, so sounds like we're code partners ken. How did you fix yours, just replace the sensor?

I feel like the car was shifting a little hard too though. I guess I need to go take it to the dealership and fork over money to have the transmission computer read?
 

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03 H6 OBW & 06 WRX Sportwagon
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trans fluid clean?

many folks have found 3 drain/fill cycles on the trans with fresh fluid, and maybe a bottle of Trans-X to help with delayed engagement and odd shifting but, P0122 could be rodent-chewed wiring or ????
 

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2004 H6 Outback Wagon "35th Anniversary Edition" w/o front bumper
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Discussion Starter #16
trans fluid clean?

many folks have found 3 drain/fill cycles on the trans with fresh fluid, and maybe a bottle of Trans-X to help with delayed engagement and odd shifting but, P0122 could be rodent-chewed wiring or ????
It's not very dirty. I just drain/filled once last spring, but that's expensive and a pain in the butt to let it drain/fill 3 times.

I'm thinking the P0122 is the sensor just gone bad or something but I don't know I haven't taken a look at it at all
 

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It's not very dirty. I just drain/filled once last spring, but that's expensive and a pain in the butt to let it drain/fill 3 times.

I'm thinking the P0122 is the sensor just gone bad or something but I don't know I haven't taken a look at it at all
I have found siphoning up the ATF fill tube is pretty painless. I measure what I pull when I loose suction, and then I just put the same volume back in.

in my case with a fancy siphon I could get a whole gallon out. which is about what is typically said here of draining the pan from below, and the rest is up in the pump. (about 2 gallons total volume on these 4EAT)

__________

when I google searched on p0122 subaru it said a TPS sensor. maybe @plain OM would have a suggestion as that can be a expensive part to buy. and I wonder if such could be the connector vs. the sensor. or something else with that code.

subaru lists the sensor as a 22633KA040 which only covers the H6 of 2003-2004. rockauto has a couple aftermarkets though. (don't know how good they are vs. OEM)

and I wonder if pick and pull things maybe a great alternative, as lots of theads here reference "possible" TPS issues but not so much data to support the swapping of that part .( pick and pulls in February sucks too).

but hope you get it sorted, as driving like this is dangerous.
 

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Not much to add . . .

P0122 is for the TPS or the wiring to it. FSM indicates that the code is set as soon as the fault is detected. Perhaps clear the codes and then see if it comes back right away, confirming that there's a "hard" TPS fault (i.e., not intermittent). Troubleshooting is mainly checking for continuity and shorts in the wiring and some voltages.
 

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isn't there a TSB for the TPS on the 2nd gen H6es?

there's a lot of TSBs listed at scoobymods.com
 

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My TPS had to be replaced, it wasn't one of the ones covered by the TSB.

They are pretty easy to measure with an ohmmeter.
 
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