This is certainly a good one! I have been thinking precisely about these kinds of sentences and I guess that they may be difficult for learners of Spanish. The gramatically correct sentences are 1 and 3. However, we Spanish native speakers also express this like 2 and 4 when talking. If you have to do an essay, I would advise you against writing sentences like 2 and 4, so steer clear of them when writing. If you have to use them when talking, I think you can say all of them. As I said, for us Spanish speakers, "Me iría si pudiera" (gramatically correct) is quite the same as "Me iba si pudiera" (gramatically incorrect). I think no one will ever say something if you SAY the gramatically incorrect ones.