Engine rumbling at low rpm

[DJay]

Over the past 2 days My 98 Legacy AT with 2.2ltr engine has developed a low
RPM rumbling. Not noticeable at IDLE but around 1000 - 1300 rpms it is very
noticeable. I can hear it and feel it.
Recently (3 weeks ago) the car's check engine light came on. The OBDII code
was "misfire on cylinder 1 and misfire on cylinder 2) code 301 and 301 (if I
remember correctly). I replaced the spark plugs (NGKs) and spark plug wires
and reset the ECM with the scanner.
Now 3 weeks later I have the low rumbling noise. The rumbling happens with
the car in park or in neutral so I don't believe it is transmission related.
The sound/feeling is difficult to describe and it is not a pinging but
rather a lower vibrating knocking sound. The sensation was such that I even
suspected motor mounts - but they are okay. The Check Engine light has
remained off.
I rechecked my plug & wires and all seems correct.
My next step is to schedule an appointment at a shop but do any of you have
suggestions on what I might be able to try?

Thanks,

Djay

 

[DJay]

Over the past 2 days My 98 Legacy AT with 2.2ltr engine has developed a low
RPM rumbling. Not noticeable at IDLE but around 1000 - 1300 rpms it is very
noticeable. I can hear it and feel it.
Recently (3 weeks ago) the car's check engine light came on. The OBDII code
was "misfire on cylinder 1 and misfire on cylinder 2) code 301 and 301 (if I
remember correctly). I replaced the spark plugs (NGKs) and spark plug wires
and reset the ECM with the scanner.
Now 3 weeks later I have the low rumbling noise. The rumbling happens with
the car in park or in neutral so I don't believe it is transmission related.
The sound/feeling is difficult to describe and it is not a pinging but
rather a lower vibrating knocking sound. The sensation was such that I even
suspected motor mounts - but they are okay. The Check Engine light has
remained off.
I rechecked my plug & wires and all seems correct.
My next step is to schedule an appointment at a shop but do any of you have
suggestions on what I might be able to try?

Thanks,

Djay

Oh the car has 80K miles on it...

 

[Todd H.]

Over the past 2 days My 98 Legacy AT with 2.2ltr engine has developed a low
RPM rumbling. Not noticeable at IDLE but around 1000 - 1300 rpms it is very
noticeable. I can hear it and feel it.
Recently (3 weeks ago) the car's check engine light came on. The OBDII code
was "misfire on cylinder 1 and misfire on cylinder 2) code 301 and 301 (if I
remember correctly). I replaced the spark plugs (NGKs) and spark plug wires
and reset the ECM with the scanner.
Now 3 weeks later I have the low rumbling noise. The rumbling happens with
the car in park or in neutral so I don't believe it is transmission related.
The sound/feeling is difficult to describe and it is not a pinging but
rather a lower vibrating knocking sound. The sensation was such that I even
suspected motor mounts - but they are okay. The Check Engine light has
remained off.
I rechecked my plug & wires and all seems correct.
My next step is to schedule an appointment at a shop but do any of you have
suggestions on what I might be able to try?

Check groups.google.com for my frustrations with the same issue with
01 Outback. Mine only seemed to be an issue in warm months. I don't
notice it anymore, perhaps I've just gotten used to it. Subaru
checked it out several times and said "no problem found." I talked
with a factory service rep about it and he described the phenomenon as
an "undesirably normal condition" that others have reported. Then
some rasonable explanation about getting the car to run well at all
temperature, fuel mixture, etc corners and that they have to recert
the car to federal emissions any time they tweak anything, etc.

Worth checking the dealer though to see if they've got more recent ECU
firmware to upload into your engine controller that might be better
though.

Best Regards,

 

[Sparky Polastri]

Try driving a little more aggressively for a few days. Mine does the same
thing, but I think its the ECU learning itself into a "this guy doesnt step
on the accelerator hard, let's conserve gas now!" mode. I mostly use my car
to get to work and back and spend my time trying to keep gas milage as low
as possible for entertainment.

The sound on mine goes away when I drive around like an idiot (like
everybody else on the road it seems) for a few days.

The sound: felt through brake petal at stop, a low throbbing hum like what a
jackhammer might sound like under 6 feet of loose dirt.

 

[darealclemshady]

Todd,

Is it all that common for owners to go to the shop and see if there are
any ECU firmware updates for their car? Does Subaru have firmware
revisions coming out a lot? If so, is this something they can program
into the unit by just plugging into it, or do they have to actually
swap out hardware like a chip, etc.?

I'm curious cause I've got a 98 Legacy Outback that I might want to go
talk w/ them about.

 

[Todd H.]

Todd,

Is it all that common for owners to go to the shop and see if there are
any ECU firmware updates for their car? Does Subaru have firmware
revisions coming out a lot? If so, is this something they can program
into the unit by just plugging into it, or do they have to actually
swap out hardware like a chip, etc.?

At least on my 01, they blow the new code into the ECU via a simple
hookup. Mine's had 2 code updates done in the normal course of
service. I think it's among the first things they check when there
are driveability concerns that don't have any check engine light (CEL)
codes associated with em.

I'm curious cause I've got a 98 Legacy Outback that I might want to go
talk w/ them about.

Doesn't cost anything to ask. They should be able to read what
revision o fhte ECU code you have in about 2 seconds with their
diagnostic scanner, and know if anything later is available.

Best Regards,

 

[Michael]

They probably program it with the diagnostic port. I know cobb tuning has a
access port thing you can upload maps for mods to the ecu on a wrx via the
diagnostic port, it will pull codes too.

Todd,

Is it all that common for owners to go to the shop and see if there are
any ECU firmware updates for their car? Does Subaru have firmware
revisions coming out a lot? If so, is this something they can program
into the unit by just plugging into it, or do they have to actually
swap out hardware like a chip, etc.?

I'm curious cause I've got a 98 Legacy Outback that I might want to go
talk w/ them about.