Misfire on acceleration and intermittent steering wheel wobble

[888]

Car is a 2002 Legacy wagon 2.5 NA with an automatic tranny and 225k miles.  No CEL at the moment, but I have a P0420 for the 02 sensor that comes and goes, has been doing it for a long time (I've had the car for 3 years and 22k miles). 

 

Problem 1 (I think I have two separate problems).

 

Symptoms are misfire type shuddering on acceleration under load and dismal mpg.  Seems a lot smoother when revving in neutral or park versus driving.  The driving version of the problem seems like something I've seen with a bad knock sensor on a past Forester 2.5 NA but it caused a CEL for the knock sensor when that happened.  Is it possible to have a failing knock sensor that does not cause the CEL?  Any other cause for this behavior that wouldn't cause the CEL?

 

Problem 2.

 

I have an occasional slight steering wheel wobble that seems to be most noticeable between 2.2k and 2.5k rpms, it settles down above and below that, at 2k or below it's pretty much unnoticeable.  Tires are new, balanced when installed as usual, no comments made about bad wheels by the installers.   Coupled with the misfire, it's tough to separate them completely when driving but a misfire should not cause the steering wheel to wobble unless I had play up there somewhere.

 

I'll get a clunking noise up front when turning the wheels slightly from side to side with the car stationary.  I'm told that is some play developing in the rack and pinion. 

 

I get a very slight howling noise from the front end that rises and falls with the speed of the car.

 

Front brakes do need to be replaced, I've had the parts for a long time but have been unsuccessful at getting the bolts loose up there. 

 

The howl makes me think wheel bearing? 

 

I'm not quite sure about the wobble.  it's been there a lot longer than the slight howl, so i think it's separate from the wobble. 

 

Struts are not bouncy and I get no noise from pushing/pulling on the wheels.

 

Any suggestions?

 

Thanks in advance.

[1 Lucky Texan]

you may have 2 problems, you may have 5 - but here's some things to check;

many people find cracked knock sensors that didn't cause a CEL. Oil in the plug holse/on wire boots will cause missing - as will bad spark plug wires (OEM wires preferred). Some folks confirm bad wires/coil at night , engine idling, by using a plant mister to spray watter on the high voltage parts - listen for engine stumbling and look for arcing.

you should still rotate front pair of tires with the rear to monitor for a change in the wobble. Check inner tie rods for play, they might clunk. Inspect the rear bushings for the lower control arms. they can clunk. Both those can make a wobble.

Noise up front could be several things but; check for air in the power steering reservoir - there should be no bubbles or foam. Ait intake filter box might not be securely clipped-in at the bottom. Wheel bearing could be bad. Not a bad idea to confirm brake calipers are sliding well.

Edited November 15, 2016 by 1 Lucky Texan

[Rooster2]

problem 1.....how long since spark plugs and plug wires been installed? Bad wires in particular can be okay at park when revving the motor, but spark will break down under load of driving.

 

Recently I had a wobble in steering that turned out to be fixed by replacing a half shaft that had a blown out outter rubber dust cover. Check your half shafts for that problem.

 

Does howling noise sound like it is coming from the front or rear of the car? A bad wheel bearing will sound like an rrrrrrrrrrrrrrrrrrrr sound, and will get louder if the bearing is bad at the front and stressed, like when exiting a freeway ramp on a sweeping turn.

[888]

you may have 2 problems, you may have 5 - but here's some things to check;

 

many people find cracked knock sensors that didn't cause a CEL. Oil in the plug holse/on wire boots will cause missing - as will bad spark plug wires (OEM wires preferred). Some folks confirm bad wires/coil at night , engine idling, by using a plant mister to spray watter on the high voltage parts - listen for engine stumbling and look for arcing.

 

you should still rotate front pair of tires with the rear to monitor for a change in the wobble. Check inner tie rods for play, they might clunk. Inspect the rear bushings for the lower control arms. they can clunk. Both those can make a wobble.

 

Noise up front could be several things but; check for air in the power steering reservoir - there should be no bubbles or foam. Ait intake filter box might not be securely clipped-in at the bottom. Wheel bearing could be bad. Not a bad idea to confirm brake calipers are sliding well.

 

thanks for the reply. 

 

this sure seems like the same problem my bad knock sensor caused on the Forester so it's good to know that can be a problem and not cause a CEL.  I'll replace the sensor and see what happens. 

 

I'll check the other items on your list and rotate the tires front to back. 

[888]

problem 1.....how long since spark plugs and plug wires been installed? Bad wires in particular can be okay at park when revving the motor, but spark will break down under load of driving.

 

Recently I had a wobble in steering that turned out to be fixed by replacing a half shaft that had a blown out outter rubber dust cover. Check your half shafts for that problem.

 

Does howling noise sound like it is coming from the front or rear of the car? A bad wheel bearing will sound like an rrrrrrrrrrrrrrrrrrrr sound, and will get louder if the bearing is bad at the front and stressed, like when exiting a freeway ramp on a sweeping turn.

Plugs and wires were replaced right before I bought the car with 205k on it, so maybe 20k ago.  It was a Goodwill donated car with a botched timing belt job but it's a Carolina car with no rust so a Subaru guy rescued it and went through everything before reselling it to me.  Has 2.5 RS heads on it as well.  Wouldn't a bad plug/wire cause a misfire based CEL? 

 

The howling is probably more a low hum that seems to be coming from the front and changes pitch/tone as straight line speed increases/decreases  I can't get it to change pitch/tone by turning side to side at speed  to load and unload the wheel bearings which is how I typically figure it out on a VW and why I'm not sure it's behind the noise I hear.

 

I was thinking maybe axle/CV joint, i need to pick up the front end and start prying on stuff. 

Edited November 15, 2016 by 888

[1 Lucky Texan]

soob bearings rarely show typical failure symptoms and can be maddeningly difficult to diagnose. Try getting the front up in the air, listen/feel at the springs and hubs (use mechanic's stethoscope) for vibration when turning the wheel. Lift/rock in the 12 - 6 o'clock direction - should be no movement. compare sides to each other. Maybe check the rear like that too.

Edited November 15, 2016 by 1 Lucky Texan

[888]

The misfire appears to have been a knock sensor, no CEL or anything else as a clue.  I'll move on the to suspension wobble next.

[Rooster2]

Wouldn't a bad plug/wire cause a misfire based CEL? Yes, very likely to cause a CEL, but still a possibility that previous owner went cheap with low cost plug wires and spark plugs. If so, the cheapies don't hold up well. Pull a spark plug, identify manufacturer, and part number to see if  from a quality manufacturer. You don't want to see that the plugs are made by Champion or Autolight. They don't work well in a Subie. Best to see that NKG plugs are in use. Probably impossible to identify manufacturer of plug wires, however, does the wire set look robust with thick diameter wires?

[888]

Wouldn't a bad plug/wire cause a misfire based CEL? Yes, very likely to cause a CEL, but still a possibility that previous owner went cheap with low cost plug wires and spark plugs. If so, the cheapies don't hold up well. Pull a spark plug, identify manufacturer, and part number to see if  from a quality manufacturer. You don't want to see that the plugs are made by Champion or Autolight. They don't work well in a Subie. Best to see that NKG plugs are in use. Probably impossible to identify manufacturer of plug wires, however, does the wire set look robust with thick diameter wires?

Wires look to be correct diameter and were new when I got it.  All of the protective covers are installed and everything looks to be routed correctly.  The guy who did the work prior to me buying it is a Subaru guy, used to wrench full time but went into something else when the economy tanked some years ago.  He rescues Subarus for fun, now.   I can't imagine him using anything other than NGK's, he had a stock of them in the garage last time I was there, but I can ask. 

 

Switched front tires to rear one side at a time with no real change.  I did see that the inner boot is torn on the drivers side axle and I can see the joint underneath so that needs to be addressed, I'll do that first and see what kind of effect that has.

[888]

It appears that the misfire was a decaying coil, that really helped with driveability other than the automatic seems to be struggling on what to do with all that extra power   Going to replace the axle soon.