Other than the clicking noise, I had similiar problems on my car and it was the crankshaft position sensor. Engine would "stumble" at highway speeds, almost like it was stalling and restarting, after which the tach would read zero rpm'*. Stopping, shutting the engine off, and restarting would get the tach reading again. Car would ocassionally stall at idle, but most times would start right up again. Couple of times the car wouldn't start until I left it sit for a while.
Does this sound like what you are experiencing?