07 Spec B Misfire All Cylinders

[SinisterMatti]

I recently purchased an 07 spec b which had spent it's life in Florida and So. Cal. It ran great when I first got it, but since the cold weather hit (I live in Montana, so 0 degrees F is not unusual)

 

I've been experiencing rough idle and Misfire on all four cylinders. I don't notice the issue and don't get a misfire code when the car is warming up, as the warm up sequence keeps the RPMs higher than usual.

 

Once the car reaches operating temperature if I don't keep it under load or give it gas the Tach will move back and forth between 1k and below 500. Sometimes it will go so low the engine sounds like it's close to stalling. If I keep some throttle on while stopped I can still feel the engine shutter, but I don't get the CEL for misfire on all four cylinders.

 

I've taken the car to autozone to read the CEL immediately after it showed up, and the codes are all occurring at the same time. The car is stock with the exception of a cobb sf intake (exact same issue was occurring prior to installation) and an AVO TMIC (stock cracked and was causing CEL for running lean on bank 1. Lean on bank 1 has not occurred since installation of the new TMIC.)

 

The local Subaru dealership is saying that this is being caused by incorrect valve clearance. They say that this only occurs during cold weather because the metal expands and retracts. According to them, once the car reaches running temperature the valves fit into place, and that is why I don't notice the issue in summer.

 

The only thing that makes me wonder about this diagnosis is the fact that the car will run rough for roughly 15 to 20 minutes after reaching normal running temperature. It also seems odd that all four cylinders are having the same issue at the same time.

 

I was wondering if anyone here had any further ideas before I dump $2000 into a valve job that may or may not fix the issue.

[apexi]

Have you double checked for any disconnected vacuum hoses? T under the intercooler? From what I've read on here, that'd be the first thing I would look for before spending any money.

[SinisterMatti]

I've checked for vacuum leaks, and didn't find anything.

[AF_3C2]

You may still want to invest in getting a smoke test done on your intake system- the fluctuating idle is very indicative of a vacuum leak, and can cause the misfires.

 

Another possibility is a fuel pressure issue- but that would probably give you other issues if it were pretty severe.

[landark]

I had a similar issue right after I bought mine. It came from Florida and the day after I bought it in February it threw CELs and the SI light started flashing.

 

My issue was the intake manifold gasket. A common problem with these.

[05 legacy gtltd]

CEL on and cruise light flashing, I have blown a vacum hose off a couple of times. Right after the short ram intake hose, the second section of intake hose there is a small hose that comes off at the elbow of second section and feeds a sensor(? maybe some one can tell us what that sensor is) that is were mine blew off two times, pushed back on, reset and seems to run ok. But there is something else going on to cause this hose to blow off. My 05 legacy gt ltd, has a small miss, at a stand still I idle up around 1800-2200rpm and I get a very small pop (misfire) now and then that I can hear, does not seem to go away no matter what the tempeture is. Just had it in to shop, changed plugs, coilpacks, still have very small miss.