1990 Chrysler Imperial Motor shaking

Do you have a digital multimeter? If so you can do an inductive test on the plug wires, engine running. You don't penetrate the plug wire insulation or take the plug wire loose. One lead touches the plug wire other lead goes to ground/ metal park of engine. You do have to watch out that you or the leads don't get caught in belts/s--pulleys or fan blade, anything. The reading is different from one vehicle to another, usually around 1/2 volt. If a couple of plug wires show zero and the others show close to the same, I'd change the cap and rotor where applicable.

Any applicable trouble codes? Also use a gage and check fuel pressure.