Cause of sputtering upon acceleration on 2002 Outback

I'd start with the dreaded EGR valve. Check it's operation and/or clean it so it has free operation, check the vacuum lines leading from the intake plenum. Butyl rubber degrades and can cause performance issues. Recommend replacing the leakies with silicone hoses from summit racing. BMW uses silicone for a good reason.

The Judge has a good point..very good, and an OBD will tell you a lot

X2 on getting the OBD codes read. If the misfire is random, it's a fuel delivery problem. If it shows a specific cylinder, it's the plug, wire or coil.

g'mornin TS....you saved me a couple bucks I need a serpentine belt...thanks every dime counts around my house

gosh darnit stickman649>>>communication is the essence of a good relationship..doncha know?

Might consider catalytic converter as well. You can use an infrared temp gun and measure pre and post catalytic. If there is a large difference in temperature, that may indicate a plugged catalytic converter. I also agree with all of the above... including the fuel filter and the ignition parts.

I'm also suffering the same problem in my Outback as well...all of your knowledge is extremely helpful, and appreciated! That said, why does mine shake like a washer on the spin cycle when accelerating?

I just bought a 2002 outback base 2.5. It stutters under hard acceleration and uses ALOT of fuel. It threw 6 engines codes.. Missfire cylinder 1 Missfire cylinder 2 Coil pack O2sensor low input O2sensor high output (or vice versa) Fuel mixture something or other Replaced coil. Check engine light is still on, problem remains.

I would start by changing the spark plugs if they at lot of miles on them.

Never in my 41 years have i seen spark plugs operate at idle, light acceleration and moderate acceleration then missfire under hard acceleration, only to smooth out at 3500 rpm. So no, i do not believe the plugs are the issue. Reading these forums many have mentioned o2 sensor. I did get 2 fault codes from the same o2 sensor however, the sensor in question only reads 1 bank. I have a missfire in both banks (cylinders 1 and 2). Tomorrow i will jack the car up and take a look underneath and see whats going on. The car i traded for this was a nissan 300zx, that car didnt run when i bought it, ecu showed crank sensor fault. I replaced the crank sensor and it still showed cas fault. This subaru is doing similar stuff. It says bad coil, i replaced the coil and i still get the faulty coil fault. Makes me think maybe the ecu is going out. I will know more after i get under the car and start checking things out. If any of you have had this problem, please let me know what you did that remedied the issue. Thx.

Ai had the same issue and after changing the coil pack I still wasn't getting spark at the coil. Faulty wiring harness? ECU? idk I'm stressed.

I had same problem changed the plugs problem solved 13.00

Great man also improved and clean all your ground wire and two more ground wire from the negative to metal parts of the engine