violent shaking in car after having oil valve covers replaced on 2001 Cadillac Catera

I recently took my car in to have the oil valve covers replaced because they were leaking oil and causing the car to smoke. I picked my car up and when I idle and accelerate my car shakes violently. The mechanic is telling me that the ignition coil is bad and so is a spark plug. I did not have this problem when I took the car in. Is my car just going bad or did the mechanic cause this problem?

Asked by for the 2001 Cadillac Catera
Each valve cover has a coil pack - basically three individual coils joined into one unit. They go into the valve covers, and must be removed to access the valve cover gasket. When you pull off a coil, the rubber insulating boots on the coils can become compromised.

I would say that the mechanic did not cause the problem directly, but the problem likely occured as a result of removing them in the first place, based on age and mileage.

Perhaps proactively they could have been included in an estimate for repairs.