I drive a 1993 Mitsubishi Eclipse.
Frequently (though not all the time), when I start the car, the engine runs fine for about two seconds, then the car will noticeably shake (you can see the steering wheel moving) for about two seconds, then the car will be just fine.
Why might this be?
Have the tires and the engine checked out. Going only by my own experience, it could be an indication of something serious (and expensive) coming on.
What’s odd is that yours actually stops shaking after a while. When mine was doing it over a year ago (I have a 1989 Dodge Daytona CS Turbo), they first thought the tires were separating, but it turned out to be a cracked engine head.
Or wait for a few more posts and get some second opinions.
Just to reitterate, the car only shakes for two seconds or so and that’s the end of it until I start the car again. Thanks for the input regardless though.
I think he is saying that his car shakes while it’s sitting still, idling, and then goes away. So, it wouldn’t be anything to do with the tires.
I think engine roughness is causing your shaking problem. But why is anyone’s guess. Worn engine mounts allowing the engine to torque more than it should? I know the 4G63 engine has balance shafts, is your car a turbo? I have no clue, really. Like, vivalostwages, I’ll wait for others to weigh in. 
If it’s shaking only a couple seconds after start-up, I’d assume it couldn’t be anything to do with the wheels. If the car is moving two seconds after ignition, it is little wonder there are problems (not saying this is the case, of course).
Maybe it’s just a tuning problem, and it’s simply that the engine is still “waking up” and the automatic choke is trying to work out what’s what. It is winter up there, after all.
Still, I’m not a mechanic, so I’ll second the advice to wait for a few more posts.
The shaking is caused by the fact that not all of the cylinders are firing correctly at that point. This can be caused by a lot of things, and is not uncommon in an engine that is 12 years old. Off the top of my head, I can think of:
oil or coolant leaking into the cylinders while the engine is at rest due to old and worn components, once it burns off the engine runs fine
worn spark plugs
old spark plug wires
worn fuel injectors
some sensor not working right which is causing the computer to get confused
I’m just a back yard tinkerer, so I’m sure the pros here can think of quite a few more things to add to the list. You could spend a lot of time and effort tracking down the problem, but unless you’ve got any other symptoms I wouldn’t worry too much about it. If you’ve never replaced the spark plugs and wires I would probably do those and see what happens, since they probably need replacement at this point anyway.
One other thought, it might be water in the distributer. Is it worse when it is wet out? If so, it’s a good bet that it’s either time for a new distributer cap or new spark plug wires.
Hmm, interesting theory. I’ll keep track of when it happens next, and if it is wet, I’ll look into that.
Anyways, thanks for the help guys. It doesn’t sound like it’s a big deal, which is good, and it doesn’t really bother me. I just wanted to confirm that it wasn’t anything serious.
Probably the Idle Speed Controller motor is dirty/failing. This is very common on the Mitsu 4G63. Also, IIRC there is no distributor on that car.
Find a web forum or mechanic who specializes in those cars (commonly known by the shorthand DSM, for Diamond Star Motors, the joint venture between Mitsu and Chrysler that built them) and ask them. There’s a fairly simple procedure for checking the electrical integrity of the ISC.
Does it do something similar when you turn on the AC?
My first thought was the idle air controller wasn’t working as quickly as it should – essentially what tadc said. It’s pretty hard to imagine that any of the other things mentioned would be fine for 2 seconds, then act up for 2 seconds, then be fine again.
Well, I haven’t tested it extensively since it’s winter and I just got the car in November, but if I recall correctly, I think the car may have behaved in a very similar fashion. I’ll check again tomorrow and update this with my findings.
Oh, and someone asked earlier if I had a turbo. I do not.