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2004 X Startup/ Idle Issues - SOLVED

2746 Views 14 Replies 6 Participants Last post by  Kevin
Hello friends,

After owning my first high-mileage forester for a bit over a year, it has finally presented me with a challenge I need some back-up for.

About a month and a half ago, I was pulling out onto a road and noticed my car hesitated badly and the CEL flashed and then resorted back to its usual solid lit position lol (evap leak - gas cap even though i just replaced the gas cap and it didnt fix the issue). Obviously this threw a red flag, so I went on to my bluedriver app and ran the code. (Misfire cylinder 2). I continued driving and observing and eventually got around to replacing my plugs and wires. (NGK)

That fixed my problem misfire issue. Hasn't happened since, car felt like it was running stronger than ever. Cool beans. Or so I thought.

Shortly after, my car developed a low idle when cold condition (temperatures in Pittsburgh began dropping significantly after the change which is why I think it is coincidental) Its quite strange. if it is lower than about 47 degrees outside, my car will have trouble idling. If it is about the 47-35 degree range the car will start, run a bit rough for a few seconds, and then settle out slightly over 1000 rpm. If it is lower than about 30 degrees, the car will start and then immediately stall, unless I give it throttle (which i will hold it at around 1500 rpm) for a few seconds and then very slowly let off the throttle and then car will idle low (around 350-500 rpm). This all goes away once the car hits operating temperature, its almost like a switch is flipped and the car remembers how to function correctly. Also the car runs great in any state other than idle.

Here's what I've done so far to try to fix the issue with help from various sources:
Removed and fully cleaned throttle body and replaced gasket with OEM
Cleaned IACV (was nasty)
Cleaned MAP sensor
Gapped new plugs
Replaced PCV (was nasty)
Replaced fuel filter w/ OEM
Checked fuel pressure (around 37psi at idle)
Replaced ignition coil w/ OEM (was getting strange primary resistance readings on the old one so i was really hoping this was the issue, but no)

I'm beginning to think my alternator might be the culprit as the issues seem to magnify when its cold and the car has a high electric load.

Next steps I was thinking:
Check/ replace alternator
Replace IACV

I'm able to track just about any OBD2 reading that the foz can give me so if there is a reading that will help clear something up let me know and i will get it for you.

I would appreciate any input anyone might have for me.

Thanks in advance for any help!

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I see this is your first forum post, so welcome to the forum from Oregon! :biggrin:

I seem to recall reading that a defective coolant temperature sensor can cause of poor idling when cold? :confused:


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['07 FSXT MODding Journal] ['03 X MODding Journal]
Hi Bobby! I appreciate your help.

From what I have seen from the coolant and intake air temp readings seem pretty good. I will read them at startup once the car has fully cooled to ambient temp and report back on my findings.
When I went to start my car this morning, these were my temp sensor readings:

It was about 26 degrees Fahrenheit outside (around 3 degrees celcius).

Intake Air Temperature -3

Engine Coolant Temperature -2

Here's a screenshot of the readings from BlueDriver

Also, I noticed that if I have my heat on full blast and turn my headlights on and off you can hear the fans change in speed. Could this be a sign of the alternator going bad??


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The coolant temperature sensor has 2 outputs, one goes to the coolant temperature gauge & one goes to the ECM. If the one going to the ECM is faulty, that could cause issues, as the ECM won't know what the coolant temperature is & the engine may stay in "open loop" longer than it should? :confused:


['07 FSXT MODding Journal] ['03 X MODding Journal]
Hmm, Its definitely worth looking into.

So the number than I can scan is a different output than the one that the ECM uses?? That's interesting.

Also I'm super surprised at how inexpensive the sensors are at around $28 OEM.
Any difference in the engine idle when the ECM transitions from open loop to closed loop? :confused:


['07 FSXT MODding Journal] ['03 X MODding Journal]
No, it seems to get better (most of the time) once the car is fully up to operating temp, but nothing on open/closed loop.
Once the engine is warmed up, the engine management should be running in "closed loop". Is your ECM transitioning from "open loop" to "closed loop" operation? :confused:


['07 FSXT MODding Journal] ['03 X MODding Journal]
On most engines there are two different coolant sensors. The one that speaks to the ECM is usually called the coolant temp SENSOR, while the one for the dash gauge is the coolant temp SENDER. The SENSOR is a common to fail part.
Just ordered an OEM coolant sensor. Should be here midway through next week. I will keep you all posted.
Curious whether the new sensor made any difference.
So, sorry for the delay everyone. Winter decided to go away for a few weeks in pittsburgh, but today it was in the low 20's and the car started without any issues! So I'm pretty confident that the issue is solved!

The new coolant temp sensor didn't make any difference, so I went with my gut and replaced the alternator. I knew some screwy things were going on with the voltage at seemingly random times, so I imagine the voltage regulator went bad.

I found a really good deal on a Bosch AL4304X on Amazon, ~$70 post core charge, one day shipped to my house for free lol. Sure beats autozone remans for $100+.

I appreciate everyone's help and advice with this issue!

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Thanks for letting us know that the fix was
Happy to see it's resolved - thanks for the follow-up. I've added "SOLVED" to the thread title.
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