I went to clean the air filter housing on my old volvo, which volvo said is made of polypropylene. the water seemed to weaken this foam that was attached to the inside of it, which just sort of crumbled out.
the foam didn't seem to add much function to the car anyway, but now there is leftover foam in the top where it was heat welded into the polypropylene housing.
these last bits wont come out with soaking, soap, or scraping with a spoon. even a razor blade wasn't much help.
i don't want it to come off over time into the engine block.
i assume it is made of polyurethane because that's what foam is generally made of? is there a solvent that will work well to dissolve it, without harming the polypropylene?