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Car: 2002 Nissan Sentra Se-r
Owned: for less than 6 months
knowledge level: not much idea about automobiles

After starting the car and running it for 2 minutes the car starts shaking and on the run the engine turns off(steering and brakes get locked). The engine sounds changes and then there is a rattling noise for 15-20 seconds. After multiple restarts the vehicle starts running smooth. The check engine soon light turns on.

The first time this happened, I took it to the mechanic and he changes all the brake rotors and brake pads. The issue got resolved and the car worked fine for 2 months.

It again occured recently and when I took it to differnt mechanic(I shifted my residence and couldnt take the auto to the mechanic who fixed the rotors) and did a complete engine diagnostic service ($99).
The mechanic noticed that the engine was low on oil (did oil change service) and hinted that if the issue happens again, the timing cover would have to be inspected for possible sludge deposit. After driving the vehicle 2 miles from the auto mechanic shop, the shaking started again(but no rattling noise or engine noise) and the check engine light turned on.

I am not sure how to proceed. I felt the engine diagnostic service was not useful. Can someone suggest what should be my next steps?

Any thoughts/suggestions would be very helpful.

Thanks.