I just replace a timing belt on an 89 predlude si and it seems to idle really bad but as far a s driving it seems fine and has plenty of power its just at idle it almost drops down to nothing we did find a little vacuum leak on lh side of the motor looks like the line broke off and cant figure out were the other side goes kind of near cruise control.

 

Either of those could be your problem. Did you line your cam gears and crank up properly when you put your T-belt on? And adjust your distributor timing with a timing light just to be safe.

I'd try to be sure about these two first, and see if that fixes the problem, as they should be done anyways. Then worry about your vacuum lines if the problem remains.

 

yeah i redid the belt and everything is lined up if i unplug the egr valve it idles normal