[JKoob]

My 2000 Forester L has been idling a bit rough on and off. Especially when started cold in the mornings,increasingly so in the last two weeks.

Finally got a CEL that threw up a P0304 code. Once the engine has warmed up everything is fine, with the occasional rough idle. I'd rather not shell out the $143 for a new ignition coil so what else should I be looking for before I go that route?

 

[FPT_RAIDER]

check your wires for any damage and check the plugs

 

[funkymonkey1002]

Has the timing belt been changed or it ever been in an accident?

It's most likely the wire or plug.

 

[good dog]

If you have a spray bottle that you can put water in, mist your coil assembly at night and see how and if the idle is affected. Pretty common for the early coil packs to go.

Any idea when the plugs and wire sets have been changed? If it ends up to be ignition related as opposed to emissions and the above items haven't been changed I'd do them at the same time.
The OEM replacement coil assembly (updated), blue NGK wire sets and plugs can be sourced from our Supporting Vendors, Grayson Subaru and Annapolis Subaru, I think you'll be happy with their pricing and prompt delivery if this is what you need.

Keep us informed as to what you find

 

[bbottomley]

Swap wires with the adjacent plug (#2) and see if the CEL changes to P0302. Or borrow a wire from a friend's Subaru and see whether it makes things smooth.

 

[JKoob]

The timing belt was changed 40K ago before I bought it.

 

[good dog]

Swap wires with the adjacent plug (#2) and see if the CEL changes to P0302. Or borrow a wire from a friend's Subaru and see whether it makes things smooth.

Even better suggestion, and you don't waste water.:lol:

 

[Real Lyte]

If you have a spray bottle that you can put water in, mist your coil assembly at night and see how and if the idle is affected. Pretty common for the early coil packs to go.

Any idea when the plugs and wire sets have been changed? If it ends up to be ignition related as opposed to emissions and the above items haven't been changed I'd do them at the same time.
The OEM replacement coil assembly (updated), blue NGK wire sets and plugs can be sourced from our Supporting Vendors, Grayson Subaru and Annapolis Subaru, I think you'll be happy with their pricing and prompt delivery if this is what you need.

Keep us informed as to what you find

That^ I had the same exact issue, a little bit of di-electric grease on the coil pack contacts fixed it.

 

[JKoob]

I'm really due for some new plugs and wires anyway so i'll give that a go first. Just replaced the front 02 sensor and the knock sensor recently with good results. I will keep in mind everyone's advice, thanks gents!