4G63 runs crappy - This is what I would do:
1)With the engine running, unplug each injector connector and plug it back in again. If the engine slows down and runs crappier with the injector unplugged, then that cylinder overall is doing its job. Test each cylinder one at a time and make sure that it isn't more than one cylinder failing at life. Let's assume you did this and found that it really is #1 cylinder misfiring.
2)Do a compression test. It should be like 150-155psi-ish in each cylinder, give or take 10%-ish. If compression is bad (like ~120psi or below), do a cylinder leakage test. If compression is good, go to step 3.
3)Swap spark plugs from #1 to #whateverworkingcylinderyouwanttostealasparkplugfrom. Now re-do Step #1.
If the misfire stays at #1, go to step 4. If not, replace your bad spark plug and love life.
4) Pull your fuel rail off and swap your injectors from #1 to #whateverworkingcylinderyouwanttostealaninjectorfrom. Be sure not to destroy your injector seals. If you destroy them, they will leak, and burn your everything to the ground. It may be smart to get the $14 4G63 injector seal kit from eBay before you do this step. Once the injectors are reinstalled, re-do Step #1 again.
If the dead cylinder moves, replace your crappy injector. If the misfire is still #1, go to step 5.
5) Go buy, borrow, steal injector noid light. Most people don't have these which is why I made this step #5 instead of step #1. If you are going to be a car-guy/gal, you may want to get a set of them because they are fun
, and you can test injector circuits like a boss. So - plug in your noid light and make sure that your ECU is pulsing your injectors. If it is pulsing normally compared to the others - you are imagining things and don't have a car at all. You are just having a nightmare about a car you once owned when you were in high school. If the noid light is not pulsing, go to step 6.
6) With the ignition on, both wires at the injector clip should have power. Make sure that they do. If not, your ECU is wonky. If they do, and your injector is not pulsing, then the ECU is not telling that injector to pulse. This would be odd because this problem never happens. Go on to step 7.
7) From my experience, either your ECU, or CAS will be the problem. I have never seen a power transistor go bad internally, and I've screwed around with a lot of 4G63's for a long time. CAS's and ECU do get weird though. Swap out each of these with other units and see if that fixes the problem. Borrow them from friends so it won't cost you anything. If neither of those fix your problem, go to step 8.
8) There is no step 8. If you have made it this far, you must have messed up the diagnosis. Please start over at step 1.
Hope that helps.