So you still have the old car and you can try swapping some parts over. I would start with the fuel pump relay.

It would be helpful if you give more information about the rough running, is there a strong smell of petrol from the exhaust when this happens, does it idle rough but pull more smoothly, etc

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Mick J
'08 Chrysler 300CRD (MB OM 642 engine)
'95 E220 estate
'89 230TE (R.I.P.)