excessive engine rumble and "harshness" inside vehicle at idle in "D"

[mwatt]

1998 Legacy Outback LTD wagon, automatic.  We've owned it since brand new; now it's got 220K well-maintained miles on it.   Over the years, more and more engine rumble and harshness (especially at idle in "D") is coming into the passenger comparment.  It's a nasty "throbbing/rumble" at idle in D.  Slipping the shifter into nuetral smooths things out a bit.......but not much.  Under the same conditions, my '99 Legacy GT is much quieter.

 

The engine idle speed is correct.  I suppose I could adjust that little throttle stop screw on the throttle body to boost the idle speed a bit but that's not really the right thing to do.....

 

I've replaced the transmission mount (thinking perhaps it had lost it's softness and cushioning) but that didn't help.  The local Subaru specialty shop has tried adjusting the dogbone (pitch stopper) and, while there was slight improvement, that throbbing rumble at idle persists.   The shop also suggested I paint a line straight across the crankshaft pulley and drive the car for a few days to see if the painted line would split apart (indicating a failing crank pulley)---but the inner and outer sections of the pulley are not separating.

 

Have any of you tried replacing motor mounts or the pitch stopper to try to fix this kind of thing ?

[MilesFox]

The vibration can be transmitted through the axle. Either the axle is owrn, or it ould be an inferior aftermarket replacement. Do some searching on this matter.

 

Idle speed can be adjusted by clocking the idle air control valve. 

[WoodsWagon]

#1 don't touch that screw. It is not an idle adjust and it leads to a bunch of other issues if you mess with it.

 

#2 make sure the engine is idling smoothly. Spark plugs should be ngk and plug wires should be OEM from the dealer. Run a bottle of Techron Fuel system cleaner though it. Make sure the exhaust or heat shields aren't bent and touching the body somewhere.

 

#3 the low stall speed torque converter means that the engine is still coupled to the wheels even at idle. That puts the pulses of each cylinder firing through the transmission and axles and suspension because the only thing holding it back is the brakes. If there's slop in any of the points between the engine and the brakes, the vibration can get worse. The normal culprit is worn CV joints in the front axles. Most of the aftermarket axles are garbage out of the box, so replacing the axles may not fix it. Subaru rebuilts are big $. http://www.ccrengines.com/mwe/ has a good reputation for rebuilt axles.

[CNY_Dave]

Try wiggling the engine and trans and listening for a contact point.

[Gloyale]

Axles.

 

This is well covered for years.

 

Replace the axle/s

[mwatt]

thank you all for the replies.  When this car had about 110 K on it, I replaced the front axles with reman units I purchased from a Subaru dealership.  Now that I think about it, that's when all of this began....and over time it's gotten worse.   Sounds like it may be time to get axles from CCR....

[Timberwolf530]

Actually, the Subie reman axles are supposed to be the most reliable.  This guy is good too.  I have both of mine from him. Great customer service and half the price of the Subies.  FYI, it's the heat from the exhaust manifold that causes the rubber to break down, so you need to keep an eye on them.  I check them every time I change oil & rotate the tires.

 

http://www.ccrengines.com/mwe/