Cylinder 1, 2, 3 missfire. Help!

[I_Am_Mike]

I have a completely stock '09 GT w 67K miles that I've owned since about 30k miles. Recently, my check engine light came on w codes for missfires in cylinder 1, 2, and 3. I'm not much of a mechanic, but thankfully I have a buddy w knowledge, tools, and a great workshop. We've been trying to diagnose what could be going on. My only performance issue is that a few months back (summer) I noticed that at light throttle, the car would hesitate a bit. That condition has very slowly gotten more pronounced, though it is still not very noticeable, except I can feel it. At open throttle there is no hesitation. If I'm cruising down the highway and take my foot off the gas and then slightly press the peddle I feel the same sputtering/hesitation that I feel when crawling slow in traffic w light throttle. We pulled plug #2 (giving me a new appreciation for the tight work that Subaru mechanics have to deal with when working on the boxer), and it showed no signs of lean or rich. Looked normal. We checked the air cleaner and noticed that when someone last replaced it, they probably didn't do enough uncopoupling and jammed it in there, compromising the seal. There was moderate dirt that we vaccumed off and resealed the filter to the plastic assembly before reassembling. Probably not a big contributor but who knows. With separate coils, it doesn't seem likely that I'm having 3 failures since I understand these tend to go quickly. We were thinking maybe some clogged fuel injectors so tonight I gave her some injector cleaner. Has anyone ever had 3 cylinders throwing a missfire code or have any other ideas of what might be going on? Any help or advice would be greatly appreciated. We literally just dumped $1400 into my wife's Jeep on Saturday so anything we can do on our own would be a huge savings. I'm afraid if I take it to a garage they're just going to start replacing plugs, coils, etc, and get expensive until they get what's actually causing this. Thanks.

[apexi]

When I see all 4 cylinders misfiring, a vacuum leak letting extra air into all four cylinders seem to be the culprit most of the time.

 

I know you have 3 cylinders misfiring, and I can't think of what would cause that. I'm leaning towards a vacuum leak, letting extra air into all the cylinders, but maybe not enough for the 4th cylinder to misfire.

 

Personally I don't think it's an injector/coil/spark plug issue affecting 3 cylinders. I'm thinking there's a disconnected vacuum hose somewhere. There's a blue T under the intercooler, and it's common for a vacuum hose to pop off there.

[Mike07LGT]

http://legacygt.com/forums/showthread.php/diy-rough-idle-cold-start-cold-temps-lgt-07-09-155325.html

 

This solved my multiple misfire issue.. not sure if it applies to 09s though

[I_Am_Mike]

Thanks for your input and suggestions. The vacuum leak sounds like it could be a possibility and that's probably where we'll start. The O-ring issue doesn't seem to follow what I've been experiencing since this hesitation at low throttle started in the summer and doesn't have rough idle. The plug we pulled didn't show evidence of running lean. Anyway, we've got some ideas to work with. If anyone else has any input, it would be very welcome. Thanks.