Within the last two months, my PT Cruiser (2006) violently shook on it's second and third startup, but not the first, fourth, nor fifth startup. Troubleshooting this with an O'Reilly employee, they suggested replacing the spark plugs or some other item (I forgot what it was). No case emerged in it's active use until within this month, I was getting an oil change, and it happened twice, but not the first two start ups. The mechanics could not figure out the cause. They weren't able to identify what caused the violent shaking of the engine. The issue was left unresolved, but the violent shaking has not occurred since then.

 

My opinion, O'Reily employees and quick lube jockeys are not mechanics and I would not rely on them for an accurate diagnosis.

When were the spark plugs last replaced and were the recommended copper plugs used? The copper plugs are to be replaced every 30,000 miles. On a related note, the spark plugs wires are to be replaced every 60,000 miles. If it is not known when this was last done it should be first to be done. Start with the simple stuff first.

Is the check engine lamp on or was it on in the past couple of months? Were any diagnostic trouble codes pulled (pending,active, and stored)? Not all codes will light the lamp.

 

Another area to examine are the ground points on the left strut tower. These have been known to corrode and cause a myriad of issues as these are major ground points for the PCM and TIPM. Be certain the battery cable terminals are clean and tight.