Hello everybody!

I have a 2001 Montero (3.5L) with 130k miles that is giving me some trouble. First, the backstory.

This weekend I did a tune up. I removed the plenum, pulled the valve covers, and replaced the cover gaskets, oil tube seals, plugs, wires, and both the upper and lower plenum gaskets. Put it all together and it was running like junk with occasional backfires. I drove to the parts store (2 miles round trip) to get the code read which showed random misfires. On the way there I could barely do 35-40mph. On the way back I lost almost all power and couldn’t exceed 20mph. This was right after a backfire followed by some “mechanical noises.” Once I got home I found the correct firing order and corrected that issue. Started it up and it idled perfectly. About a block down the road I lost power and an extreme whine started. It begins just above 2000 rpms and gets worse the higher the rpms go.

Back in the drive way I quadruple checked all vacuum lines with no issues. I searched for hours for a leak but couldn’t find anything. I located the source of the whine to somewhere very near or underneath the drivers side valve cover. Eventually, I began to dig deeper. Here is a list of what I’ve checked.

- Pulled serpentine belt and started the engine. The whine persists.

- Concerned about the misfires I pulled the timing belt inspection covers and verified timing was correct (there is still a slight misfire at higher rpms). Compression felt strong while I was manually turning the engine.

- Sprayed starting fluid near all known vacuum connections, lines, and gaskets with no changes in idle speed.

- Pulled the plenum and drivers side valve cover again. Discovered the shop who did my timing belt 10 months ago pushed the old camshaft seal into the crankcase and then installed the new seal. The old seal had wedged itself on the camshaft. Removed the old seal, inspected for internal damage/debris, and put everything together with proper torque specs. Whine and power loss persists.

What am I missing? The whine literally sounds like a chimpanzee; very loud and very obnoxious. There is also a sucking noise coming from that general area on the drivers side but I cant find anything to indicate where. I’ve searched and searched for a connection or hose that I missed upon reassembly but there just isn’t anything.