So I recently changed my timing belt and water pump on my 97 Civic LX with a very adept friend's help. The timing belt part came out fine, no knocking or anything, but I'm not so sure about the water pump or the idle. When we first started it up, the idle wandered all over the place and then settled at like 300. It never died, though. I should probably mention that we also changed the PCV valve. But as for the real problem--

There's a rapid irrhythmic click/rattle when the engine is warm and I floor it off the line, or when it's under a load like going up a hill or accelerating through the mid-RPM range with the throttle half-open or so. When I downshift at speed and floor it hard, it the noise goes away, and it doesn't happen above, oh, 4000 rpm or so.

I'm almost positive the noise is coming from the water pump or crank pulley, since we replaced the water pump and had to remove the crank pulley to get to all this. I'm not going to tear it all down again just to look, and I'm not taking it to Honda so they can charge me $700 to tell me I need to replace something I just replaced. Help?

 

Sounds like the tensioner might not be adjusted properly and the timing belt may be installed with a cog/tooth off from where it's supposed to be.

 

For the idle problem, it sounds like you didn't burp the coolant system.

You may have filled it until it overflows, but after you start the car, the level drops substantially as the coolant displaces all the air stuck in the block. If you don't turn the heater on and let the car run with the radiator cap off until it's completely warm while periodically topping it off, then it's likely that the coolant level dropped below the coolant temp sensor... and it will run like shit.

 

listen to these guys, those are both the exact explanations I would've given for your problems.

 

PS: Welcome to HAN, rubberneck!