1995 Other Nissan Models knock and egr sensor code

I have 1995 Nissan Quest van and the van had water leaks under the intake manifold on the top of engine from heater bypass hoses so I replased the hoses and fixed this problem by taking out intake manifold befor this I didnt have any check engine light, but after i did this job my check engine light poped up the code was EGR and KNOCK sensor so I took intake one more time and replaced KNOCK sensor with new one but i still have the code the check engine light what that could be?
thanks