Cars engine was replaced recently and at first check engine light was solidly on and had a bit of a shake during idle but I drove about 30 miles to pick up some things and now the check engine light flashes and the car shakes more. The catalytic converters is already messed up from the old engine also had a misfire on all cylinders. Could it be due to the old cat?
My car has 125 miles.
My car has a manual transmission.
If your catalyst is bad then I would suggest replacing it first and then clear codes and see how engine runs afterwards and if it needs further diagnosis.
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