Bent valve 2.4L - lean, rough, no power

Hello, first-time poster here.

2000 Tacoma 2.4L 2RZ-FE 2WD Manual 127k miles.

My dad and I are currently replacing a bent exhaust valve after finding low compression (90psi) on cylinder two. I've been on this forum reading about bent/burnt exhaust valves associated with symptoms of no power and rough idle, and lean conditions. It seems that there is no good answer as to why these engines are creating these issues. I'm here to share what I'm finding (work in progress...) and to see if any of you have gone through similar situations.

Bought back in October 2019 with 114k miles. Since then MAF, upstream O2 sensor, IAC valve, fuel filter, and fuel tank have all be replaced. (Rust found in tank and original fuel filter)

My problem is an occasional rough idle, especially after filling up on gas (charcoal canister and gas cap being considered...) and shutting off after driving for a while then starting engine again. Low power in each gear, including fifth, is an issue as well, but does clear up while driving though randomly. This has been going on for several months and the aforementioned parts were replaced to try and fix this problem. Still it periodically did not run smoothly.

A week ago or so I brought my truck home after a snow storm and my Dad immediately noticed that it was only running on three of the cylinders. I ran the truck hard in first trying to get up a snowy hill in RWD before that drive (did not go well) and later played around like a fool in parking lots sliding around, and eventually took it on that long drive home. I was not easy on it recently is what I'm saying.

Cylinders and pistons all seem to be in good shape as well as all other valves but the single exhaust. What's the deal? Is this just to be expected at this mileage without any head work?

I attached some pictures of interesting details. Note the cylinders being at TDC but the crankshaft punchmark being WAY off of zero degrees, and the gas/oil gunk on the intake manifold (suspected from the breather).

 

Lots of parts cleaning and valve lapping later and it is all buttoned up and running smoothly. I'm still not sure where the fix to my rough idling/running issues came but here's what I did.

First and foremost I replaced the bent exhaust valve and lapped it in and did the same for all of the other valves (new shims for all 16 buckets of course). The intake manifold and breather tubes had black, sticky residue that I cleaned out. We also noticed the old intake gaskets were worn down through the black coating to the metal (maybe small are leaks were entering here...) so these and all other top end gaskets were replaced as well. The MAF and upstream O2 sensors that I previously replaced were replaced again (a few weeks later) but this time with Toyota brand. They may have been the cause of my lean codes that I kept getting. New fuel filter as well.

That's what we fixed that we believed was necessary but I'm not sure which of these was the real culprit still. The check engine light came on a few times for lean conditions after but then cleared itself each time and has since stayed off since the O2 and MAF sensors were replaced with factory versions. This tells me that the aftermarket sensors I had on before were not working well with computer. The factory versions were expensive, especially because I have CA emissions, but were worth it.

 

Glad you were able to solve your issues and thanks for actually posting the solution!

The exhaust valves on the 3RZ get tight over time. They should be checked every so often and adjusted if needed. I checked mine the first time at 175k miles and almost all were out of spec.
It sounds like it was a combination of things that lead to your rough/low idle conditions though.

The black sticky mess is from the PCV valve. You can add a catch can if you want to prevent that gunk from getting back into the intake, otherwise you have to clean it out every so often.

 

I have a jdm motor and haven’t check valve shims yet, motor is suppose to be around 60k so?