KA24DE won't stay in time

[InsanityInc]

I have a 91 240sx, 200k miles give or take. The damn thing wont stay in time no matter what I do. I disconnect the throttle position sensor, start the car, change the timing, shut it off, reconnect the sensor, start it up again, and the timing jumps around a little bit then comes back to normal. Stays there for about a day, getting progressively more out of time as the day goes on.

Sometimes at stoplights, you can feel the thing start to go out of time as it'll be smooth, and all of a sudden, the steering wheel and shifter jerk a little bit and the idle changes, then it immediately goes back. Check the timing, and sure enough it's off.

The car also has a problem where when you start it up, it dies unless you hit the throttle to bring it up past about 1500 rpms. I assume the two problems are somehow related.

Anyone have any idea what either of these problems could be? I've tried quite a few things to correct the latter problem.