Hello, I just completed a swapover from a 2.5 to a 2.2L on my 97 Legacy Outback. That went well, but then the fun has started. Got a ****** eng light within the first 10 miles. Bought a scanner, got P0135, P0303, P0430, and P0425. I have replaced precat o2 sensor, knock and cam sensors. And also replaced the plugs and wires. (NGK splitfire, NGK wires) Car runs alot better now, it did miss badly before. Now it will run flawlessly for about 15-18 miles, but then the dang thing starts idling rough and resets the P0303 code. I also swapped a different fuel injector out of the 2.5L motor into the car on cyl #3 but the P0303 came back again . AAAARRRRGGGGG ! What are the other possible sources of missfire? Car runs pretty good now , reasonable power but does idle rough when hot. Any help or suggestions would be greatly appreciated :-\:-\

If it were my Soob, I would run a compression test and a vacuum test. It may reveal something...

 

I'd also suspect the coil pack. It may be on its last leg.

 

In the pitch black darkness, while the engine is running and at operating temp, spray some water (using a mister/sprayer) around the wires and coil pack. If you see arcing you have found a potential source of your misfire.

 

Just my 2 cents.

 

Good luck!