oops... sorry about that, i started to edit my post and got sidetracked.... 20 minutes later i sorted it out. Silly distractions!
OK, now that I know it's a 31, I'd also like to point you in the direction of the fuel pump.
My car did a lot of strange things similar to what you're describing, it turned out to be the fuel pump.
The problem was intermittent, and went on for over a year before it died properly.
Have you noticed if the fuel pump noise has changed at all recently?
1/ check timing
2/ check fuel pump
3/ check cas
4/ check afm
I'll also throw in a recommendation for you to check the distributor cap and rotor button.