1999 Honda Passport issues...

[THenningsen]

My wife's '99 Passport is down. She called the other day and said that the motor made a bad noise upon startup and all the antifreeze poured out the bottom of the motor. I got home and started taking everything apart. Finally I found that the water pump housing was cracked in half, causing the leak. New water pump, new timing belt, everthing back on. Started it up and the idle was rough. Lot of motor vibration at first, then things kinda smoothed out exept on acceleration. When I accelerate to about 1000-1200 rmp, the engine sounds like a diesel. Sounds like it is a low end knock, not up in the valve area. Once it gets faster than that, the vibration/noise goes away. After some troubleshooting, I discovered that the noise goes away when the serpentine belt is removed. I replaced the tensioner pulley, but it didn't help. Only other things that run on the serpentine is the idler pulley, A/C, power steering, alternator, fan pulley, and crank pulley. Any ideas what the problem is? Also, the check engine light is on.