Chrysler Repair: Cirrus shimmy almost too much to keep on road, brake rotor, hands off the wheel

Question
My Cirrus is doing this shimmy and shaking thing that is making it difficult to
drive. When I take my hands off the wheel, the wheel is visibly shaking all the
time and I can feel the car shimmying from side to side. At times, the front
end shaking makes it hard to keep the car in the lane. 3 months ago, I had
the computer replaced. The mechanic put in the wrong computer because it
is what he had in stock and he said it would cause no problems except a kick
when shifting. I believe the computer was for a caravan. Also, the ABS light is
coming on, but I can't recall if that coincides with the shaking problem so I
don't know if that relates. I do have a check engine light on, but I thought
that was due to the wrong computer. I am wondering if the wobbling and
shaking could be a warped brake rotor or if maybe it is a motor mount issue.
Do you have any ideas?

Answer
Hi Dawn,
If you put the car in neutral while you are moving along does the shimmy continue? If so, then it does have to do with the brakes/rotor or front suspension. If not, then it has to do with the engine power output being uneven or something to do with the transmission/output shafts.
You didn't say what year of Cirrus this is but you would do well to have the fault codes stored in the memory of the engine controller readout. An Autozone parts store will often do this for free. If you have a '96 or earlier then you can do the readout yourself using the ignition switch. So let me know if that is the case.
When you get the readout, ask the fault code number(s), what they mean, what they propose to do, and how much it will cost. Then write back and we'll compare notes.
Roland