How normal is it for my car's engine to bust out two or three big shakes after a cold startup (below 20F at least). It's done this for a while. No problem starting at all (knock on wood), and it doesn't seem to have an audible knock. After it sits for 15 or more hours, it REALLY shudders even though it starts easily. Usually it just gives one or two big shakey surges and then continues on smoothly. I'm not an expert at identifying unusual sounds, but at idle it really sounds fairly smooth even while warming up. It does vibrate some, but I had the motor mounts replaced just last week and the vibrations have noticeably reduced at warm idle and upon deceleration (where the vibration was before). Once it's warm, no shaking on startup. But after it sits for a long time it tends to do this even when it's not terribly cold out (I'd estimate it does a shake or two at any temp under 40). It much more noticeable though when it gets really cold. Sometimes, like today, it will shake five or six times and then continue on smoothly. Is it misfiring? Is this a problem? Or is this just a matter of "it's a diesel, it's old and it's cold ... live with it"?

Adding as an afterthought, the shakes happen after I have turned the key and let go of the key ... rather than DURING startup.

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