If it’s running bad you can in plug one side of UVCH with it running and if no change in how it runs pretty good chance to be IDM. Yeah they are a pain to mess with and can’t imagine having to do it in the van.
Does yours not have the fuel bowl filter in the valley? That’s the only one mine has. I done away with that stupid shower head looking pickup in my tanks and just ran a piece of fuel line to the bottom.