Subaru Forester Owners Forum banner
1 - 9 of 9 Posts

·
Registered
2009 Forester XT Auto
Joined
·
7 Posts
Discussion Starter · #1 ·
When coming down in speed, engine stumbles a bit. No apparent issue when at constant speed. Only happens when I come off of accelerator to reduce speed, and then with the initial tap of accelerator to continue at slower speed. Any thoughts.
Note, engine did throw codes 301/303 a few months ago. Cleared codes to see if would show up again. Hasn’t yet but still have stumbling issue. More of a nuisance, but would really like to fix.
 

·
Registered
non-subaru
Joined
·
911 Posts
Automatic?
When that happens, does the RPM drop below normal, like it is about to stall?
If it doesn't, maybe it is a weird artifact from the transmission.

About the p0301/303 codes, those are related to misfiles in cylinders 1 and 3. They are both on the same head, which may not mean much in itself.
While it may not be the source of your problem, an 09 may need new wires, plugs.
 

·
Registered
2009 Forester XT Auto
Joined
·
7 Posts
Discussion Starter · #3 ·
Automatic?
When that happens, does the RPM drop below normal, like it is about to stall?
If it doesn't, maybe it is a weird artifact from the transmission.

About the p0301/303 codes, those are related to misfiles in cylinders 1 and 3. They are both on the same head, which may not mean much in itself.
While it may not be the source of your problem, an 09 may need new wires, plugs.
Thanks for the quick response.
Yes automatic, and yes rpms drop below normal, almost feels like getting ready to stall, but if I lift off accelerator slightly and re-apply it goes away. So, not transmission, definitely engine related. Not sure if fuel or electrical related. Have had plugs replaced but not wires. Had suggested coil packs to my local Subaru service manage. He and I have talked a number of times regarding this. Presently, chasing cleaning fuel system and injectors. Four fill ups with fuel system cleaner applied, and still having issue. he has suggested we wait and see if it throws the 301/303 codes again, and that I not clear the codes so that his folks have a better look at the source.
I’m more inclined to think this is fuel system.
Any further thoughts on your part?
 

·
Registered
non-subaru
Joined
·
911 Posts
Thanks for the quick response.
Yes automatic, and yes rpms drop below normal, almost feels like getting ready to stall, but if I lift off accelerator slightly and re-apply it goes away. So, not transmission, definitely engine related. Not sure if fuel or electrical related. Have had plugs replaced but not wires. Had suggested coil packs to my local Subaru service manage. He and I have talked a number of times regarding this. Presently, chasing cleaning fuel system and injectors. Four fill ups with fuel system cleaner applied, and still having issue. he has suggested we wait and see if it throws the 301/303 codes again, and that I not clear the codes so that his folks have a better look at the source.
I’m more inclined to think this is fuel system.
Any further thoughts on your part?
Since the dealer is helping you, I would have to assume they looked at fuel pressure, etc.
For them, it would be a low hanging fruit to try because they have the tools and do it all the time on Subies, no doubt.

That stumble can be recorded with the right equipment, which Subaru dealers definitely have in their arsenal. Have they taken it for a test drive, seen it happen and have they had a diagnostic tool plugged in at the time?
 

·
Registered
2009 Forester XT Auto
Joined
·
7 Posts
Discussion Starter · #5 ·
Agree. Though I am uncertain as to what specific tools they have used thus far, or what they have done. A bit frustrated. Is there any trouble shooting you can recommend I do in advance of bringing it back to the dealer?
 

·
Registered
non-subaru
Joined
·
911 Posts
A free thing to try is to disconnect the battery and leave it disconnected for a little while - like 10 minutes.
Then reconnect it and restart.
It will likely take three times to start the car. Subarus always do.
When it starts, don't drive it - just let it idle for about five minutes until it idles normally.

The car finds its idle and associates the throttle position sensor at rest with it. That takes a couple of minutes.
Then see if that issue is still there. Edit: it may disappear and come back. That could be a clue.

A Throttle Position Sensor (TPS) is kinda like a volume control that gets read by the computer and it interpolates that reading to an engine speed, simply put.
If could be that the TPS wore out slightly since the last time the battery was installed so when you let go of the throttle, the computer reads a number it doesn't quite know what to do with.
It is conjecture but worth trying. I've seen this sort of issue on a Honda and recycling power made it work.

Edit: weird the dealer didn't look at this, tho.
 

·
Registered
2009 Forester XT Auto
Joined
·
7 Posts
Discussion Starter · #7 ·
A free thing to try is to disconnect the battery and leave it disconnected for a little while - like 10 minutes.
Then reconnect it and restart.
It will likely take three times to start the car. Subarus always do.
When it starts, don't drive it - just let it idle for about five minutes until it idles normally.

The car finds its idle and associates the throttle position sensor at rest with it. That takes a couple of minutes.
Then see if that issue is still there. Edit: it may disappear and come back. That could be a clue.

A Throttle Position Sensor (TPS) is kinda like a volume control that gets read by the computer and it interpolates that reading to an engine speed, simply put.
If could be that the TPS wore out slightly since the last time the battery was installed so when you let go of the throttle, the computer reads a number it doesn't quite know what to do with.
It is conjecture but worth trying. I've seen this sort of issue on a Honda and recycling power made it work.

Edit: weird the dealer didn't look at this, tho.
Thanks. Will give that a go. Will advise. Cheers.
 

·
Registered
2009 Forester XT Auto
Joined
·
7 Posts
Discussion Starter · #8 ·
Accomplished recommended fix. So far so good. Will give it a few days to see if stumbling reoccurs. Thanks.
 
1 - 9 of 9 Posts
Top