atze,
Sorry that you are seeing this issue. The problem might happen if you have large JS files opened in the editor.
Are you working with large JS files?
You can tweak the performance of tern engine from Window > Preferences > JavaScript > Performance page. Increase the performance setting either for your project or globally. Change the scope to work only on a single file (as opposed to the entire project) or turn Tern off entirely.
You can also exclude large JS files from project’s JavaScript > Include Path. Right click on the project > Properties > JavaScript > Include Path and switch to the Source tab. Expand the project entry and click the ‘Excluded’ node. You can ‘Edit’ it and add the individual files you want to remove from validation. You can also select folders containing JavaScript that you do not actively work and/or folders with a large number of JavaScript resources.
Hope this helps.Please let us know how the suggestions work for you.
–Swapna
MyEclipse Support