Hey all. Been trying to figure out an issue with my Pops '99 Montero. A while back the engine developed a loud knock, which even with a stethoscope my brother and I have been unable to pinpoint. We figured that a lifter went south, and since the truck showed signs of worn valve stem seals, we tore into it last weekend.

We replaced all the VSS and the lifters, and new gaskets all around. Buttoned it back up and the knock still remains. So now we are at a loss as to where to look next. The strange part is, the knock is only present at idle, and as soon as you give it some gas, it goes away. Some other info I have:

Timing belt was done by the PO approx. 8K miles ago. Documented with receipts from the mechanic.

Power steering pump developed a leak a while ago, ran the engine without the belt to see if the PS pump was shot. Noise is still there.

He blew a coolant hose a while back on the way to my brother's house. He got it there, but the engine got hot. He says it stayed in the normal range for a while, but by the time he got there the temp gauge was all the way up. After this is when the engine knock appeared, so I'm wondering if maybe the water pump is on it's way out.

That's what I know so far. Any tips or possible causes would be greatly appreciated.