To me there are two different problems with rhythm. One is going slower, faster, slower and so on. The second one is the problem of doing things like "Boom-uh-da-chicka-chicka" and so on the right way i.e. problems related with concepts like 'swing' or 'drive' (don't ask me to really explain what that is). I have not yet figured out what problem you have, Jo, but I think that pointing out that difference may be helpful in some way.
Imagining that both of those problems can be solved by using a metronome is REALLY difficult to me. To learn what e.g. 'swing' is does not really require to play your music exactly even-spaced as a metronome wants to force you to, so it will only confuse you. But once you have learned to perform the rhythm you will easily be able to adapt to a metronome if required.
Telling you that the only way is 'feeling' would be too abstract, although it's true. Whenever you hear a song with some rhythm you like try to transform that rhythm in some kind of physical motion, not dancing, just some kind of swaying, even if you just do it in your imagination. Later when you want to reproduce that rhythm, try to get into that physical motion first and then start to play the song. Look at professional musicians: they're all moving (except of those who are trained to obey conductors, but in this case the conductor must move instead :-> ).
Hehe - seems like someone must move. If you're alone it's up to you.
kendall - I remember playing 'Me & Bobby McGee' once, and there was a harmonica player, quite good, but something was wrong, something was wrong... Took me several minutes to find out that he was playing the same song, correctly and with great feeling but exactly AT HALF SPEED. Yes, there are people who can do things like these, but I'll never be able to figure out how.