One time my wife's brother had a car that supposedly his ex dumped something into the gas tank, and then the car wouldn't start. Cranked over fine. Of course we got the tank cleaned out and replaced the fuel filters. He got someone to test the "gas" we drained out. The report was antifreeze was dumped into the tank, and it was suggested that we pull the intake and clean the intake passages. The sticky, gooey stuff in the intake ports sort of cleaned up with water on a rag (you had to work at it with the wet rag, it was a mess).

The word was that if the antifreeze could have burned inside the combustion chamber it would have effected the pistons and rings much like blown head gaskets do. According to the place that did the test, we were fortunate that who ever dumped the antifreeze into the gas tank dumped in too much and diluted the gas so it didn't burn.

I have no idea how much of the story about the fuel test was factual, but the sticky stuff in the intake was correct. With the tank cleaned up, new filters, the intake manifold cleaned up and fresh gas the car ran great.