Hi there,
My car- 97 lagacy L nearly 140000 mi, has a noise when start, especially in cold.
checked with youtube videos and very similar to someones' which was diagnosed as piston slap, but i am not very familiar with this problem.
is this very bad? the link for your refernce: http://www.youtube.com/watch?v=p98Aq...eature=related
is there anyone has this pro?

Piston slap is not too common with the EJ22, but it is possible. Especially with this year engine. The Phase II EJ22 had shorter piston skirts, and to the best of my knowledge the pistons were made of a different alloy than the Phase I. Piston slap is when the clearance between the cylinder and the piston increases. When the piston travels down the cylinder during combustion, it cocks sideways a little and the skirt of the piston comes into contact with the cylinder. (Continued...)

When the engine warms up and the materials heat up and expand, the noise generally goes away. Phase I EJ22 engines have longer pistons than Phase II engines, making them less prone to piston slap. Don't be discouraged, the car can still last, but chances are the piston slap will wear down the cylinder walls at some point, increasing friction and reducing compression. Just make sure you let the car warm up before putting any stress on the engine (Driving the car). The noise might not even be piston slap, for all we know it could be a noisy lifter, since the Phase II engine no longer had hydraulic lash adjusters. You might want to give the car a valve job to see if that makes the noise go away before you worry about piston slap.