I went to check the timing on my 88 Maxima because of the lack of performance and fuel mileage, and rough idle, and found that it was off...severely off. If the first notch on the left is 0 and the last is 30, the pointer would have been at about 45 or 50. I adjusted it by turning the distributor but even when I get it as closely lined up as possible to the stationary pointer, it still "jumps" and appears jittery under the timing light, and sometimes it still idles rough. (However, adjusting it made it sound better) I put all new bosch platinum 2 plugs, borg-warner cables, and a new cap and rotor on the car in late spring. I'd like to know if a little jump and jitter is normal under the timing light, and if not, what needs to be done. I will note that the drivebelts and timing belt are really cracked and worn, and say "Nissan" on them, which leads me to believe they are the 14-year-old factory belts. But that's another paycheck.

 

Cross your fingers and save your pennies...that thing going to break. Then you are going to have a mess on your hands. Allot of things can cause a jittery timing light but a slipping timing belt will cause the car to (jump) timing which is what I suspect as you said your timing was WAY off. If the car has jumped timing because of a timing belt slip then it is not very long until the belt goes altogether. If you don't know if the timing belt has been changed within 60k it needs to be done or else you are risking catastrophic engine failure...bent valves, cracked head, and busted pistons. I don't want to tell you the car is drivable or not (that is your risk to take) but if it jumps timing again, park it and call a tow truck before she blows and consider yourself luck for the warning...most just snap or slip till BOOM! Not being there to see and hear the motor I cannot be 100% certain of your problem but the cracked timing belt is SCARY and could very easily be the root cause of the symptom you are experiencing.

 

Ive been there but it was my tensioner. Its recommended when changing your timing belt to do the tensioner too. I changed the timing belt and didnt know about the tensioner change until after it shattered. I needed new heads and some other things cost me 1500 to get fixed.