Misfire cylinder 4, it can get pretty severe. Violently shaking the van.

We haven't tried anything else. Chang the oil will relieve the problem but it doesn't fix it, out comes back in a few months. I'm curious how/why changing the oil would cause/prevent a misfire.

That is very odd, we had vehicles in the past with massive amounts of sludge and by flushing oil it would help with oil pressure but this doesn't sound remotely similar, sound like possibly a coincedence? If you can't figure it out feel free to bring it by our shop we will do our best to get your car back running good, we are located in Federal Way. Thanks and good luck