Bob,I'm right there with you. I struggled with rhythm and timing for a long time -with the same results that you have. I thought that I would never get it and then one day it clicked. It was like a light went on a I got it. I'm still not great, but I'm much better, I can find the beat when listening to music, I know when I'm off, I can play along, etc.
Here are some things that I did along the way that helped me:
1. Make sure you're solid on your music theory with respect to rythm and timing. Know what quarter notes, 1/8 notes, downbeat, upbeat, 4/4 time, etc. mean. This will give you the confidence that you are doing things correctly when you listen or play along. If someone says "come in on the and of 3" you know that there are 3 eighth notes until the full measure starts, etc.
2. When listening to music try to count the beat. I found that saying 1-and 2-and 3-and 4-and helped. Pick a song that has a distinct beat and see if you can count along with it. I now play in a band so my role as the harp player is "odd job". I picked up a tambourine and play that on a couple of songs and you have to stay with the rhythm otherwise it sounds really bad. Listen to "All Over Now" by the Rolling Stones - the tambourine plays on every upbeat - that's the "and" portion of the 1-and 2-and etc.
3. Once you find the beat on a song that is distinct, then try finding it on songs where it isn't as distinctive. You'll find yourself counting off the beats and listening to things that you didn't notice before. For example, many of the Beatles songs that use tambourine hit it on the 2 and 4 downbeats. As you listen to music begin to listen to parts of the music such as the snare drum, the bass drum, the bass or other accents. These will usually help you find the beat and understand why a given accent gives a song a differnt sound - added syncopation on the upbeats or 2&4 or added pulse on the downbeats or 1&3.
4. Tap your foot. People told me to do this, I tried, but it was of no use until I could get through steps 1-3 above. If you can't find the beat in your head or in your bones, then tapping your foot just adds confusion. Pretty soon you will not be able to listen to music without tapping your foot.
I hope this helps, good luck,
Alan
The good times last forever
The bad times fade away