wandering timing marks
 

In trying to set the timing on my 88 convertible using an inductive type timing light , I noticed that the timing marks were wandering around making it impossible to set correctly. I'm thinking I have worn bushings in the CAS. The engine has roughly 160K on it. Is there any other possible cause that comes to mind?

Vacuum leak or TPS.

You should fix those first then set timing as per the FSM. You need to jump a check connector

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Like he said, first check by going through the manual. Most of the time, fluctuations are vacuum or throttle position sensor related. Something you might want to do is to make sure that you adjust the timing slightly, then turn the vehicle off and on again. Sometimes they don't like to take a whole lot of adjustment at once. There is also a spot in the FSM for checking the crank sensor. If you have to keep resetting your throttle position sensor every time you cycle the power, then you can possibly have electrical gremlins.

Thanks for the input.

Another thing no one mentioned is that the OP may want to check the timing light itself - especially if it's one of those inexpensive plastic inductive pick-up lights. Sometimes these cheaper timing lights will false trigger from induced EMI currents from nearby plug wires, giving the false impression that your timing jitters. This effect is often worse when using such a light on a rotary, as the leading & trailing plugs fire within a few degrees of one another.

The OP didn't mention how the engine's idle quality was when he was trying to measure & set his timing, but if it was really as jittery as he describes it, it would not have a smooth & consistent idle, and he would probably would have mentioned a rough idle if he noticed it. Hence my comment to validate your test equipment works properly before assuming the car under test is broken.