See I am not sure how computer controlled that engine is. I am somewhat familer with the older 603 and the later 606, but I skipped that generation. I *think* the injection pump on that thing is pretty similer to the older 603. And for a rough idle on an older 603 I would start with delivery valve seals, and having the injectors checked.

You need to get a FSM to see how that IP is controlled and what could cause a rough idle like that. That could have a system somewhat like the 606, in that case it could be a sensor.

I wouldn't bother with a compression test. Has it been burning any oil? Does it start up right away when cold? Pop the oil cap and check for blow by. If these three things come back good the compression is fine.

Before checking compression I would check IP timing. I think you use an RIV light on that engine for this, but am not sure.

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1969 280SE
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