I just thought I would share my recent experience with my Toyota 4Runner. Purchased it about a year ago at 184k miles. I couldn't pass up the 2.7 equipped with the R150F 5-speed. Once it hit 190k I started having a slight misfire on cylinder one. (CEL produced a code for that cylinder).
Odd thing was that it would only misfire on startup and then it was done.

-So I replaced the plugs (they were all warn badly).
Still misfired..
-Replaced the fuel filter
Still misfired..
-Swapped the coils on 1 and 2
Still misfired on #1...
-Changed my oil and did an oil sample and found fuel In my oil, as well as some metal above normal.
-Changed my #1 injector
Still misfired..

So at this point I felt pretty defeated and the misfire kept getting worse and eventually the engine would hardly run. So I took it to a trusted shop. They found 30 PSI in cylinder #1... Danget
Exhaust valve is burned badly

So I purchased a new head with all new valves and a new cam. Pretty slick setup if I may say.
Bought a cylinder head gasket kit from Fel-Pro and took it to them
Also had them do the rest of the injectors while it was apart.

Got the old head back and found the exhaust valve on 1 was cracked down the center and rammed into the head pretty bad.

After about a week of waiting I got her back and she is running strong now with no issues. Fuel mileage is up about 5 mpgs which I am jacked about to say the least. I'm at about 194k right now and I am planning on taking my 4Runner to 300k. I will likely never sell this vehicle I love it so much. It is in excellent shape especially for a WI vehicle.

Before anybody gets in my case about "guessing" with parts please hold off. I am a full time diesel mechanic at a Peterbilt dealer who is certified on both Cat and Cummins engines. I do know what I am doing and the parts are cheaper than the labor of Someone else looking at it. Also I didn't do the repair myself due to I live in an apartment.

I hope this helps someone else who is sharing the same issues! It seems to be a common issue in CYL 1 of this engine. Please let me know what you guys found or if you had the same problem!

Cheaper than a compression test?

Well I figured if it was a compression issue I would basically be screwed and would need to take it somewhere. I guess I didn't want to even face that as a realty. Looking back it probably should have been done when that spark plug was out....

The internet says 3RZs need their valves checked regularly.

I'm guessing it's true 'cause EVERY 3RZ I have found at a wreckers was missing it's head. I'm betting they were used by people who didn't pay attention to theirs the first time.

Speaking of valve lash, does anyone know how often that should be checked in the 2.7 and 3.4? I'm coming from the world of Hondas where it's supposed to be checked every 20,000 miles.

EDIT: scratch that. I found it.

Yeah based on the service records the previous owner gave me (which were complete since the vehicle was new) I would bet that it was never done which is why my valve burned to shit.

I have a 3RZFE with a P0301 cylinder 1 misfire at 200K miles, flashing CEL, which suddenly happened, just today.

Google found this thread for me, where I'm just starting to figure out what it might be. I know enough to check compression and to check/replace/switch the coil packs &/or plug wires &/or plugs, &/or fuel injectors but I didn't know that the valves needed to be checked/adjusted.

Can you tell me more about what is involved in checking/adjusting the valves (as I doubt they were ever checked and/or adjusted)?

I've seen it enough times that I would 100% always check compression before spending any money chasing a misfire on a RZ motor. I've seen broken valve springs, cracked heads, bad head gaskets and burnt exhaust valves all cause the same symptoms you're chasing and all would be identified by a compression test.

It's unfortunate because the motor is so great, but these relatively common issues are a nail in the coffin typically costing $800 in just parts since a new head is usually needed.

Side note, OP your transmission is a W59, R150's came behind the V6 all the 95-04 4cylinders came with the W59

Sent from my JSN-L23 using Tapatalk

Thank you for that advice to check compression first where I would normally have done compression near the end of the process of replacing the plugs and wires as while the plugs are out, you routinely check the compression at that time just before putting the new plugs in.

This did happen suddenly, not gradually but I was coasting for a while before it happened, and I only noticed it when I accelerated onto a highway ramp.

I should have mentioned there were actually 2 DTC codes, P0300 & P0301, but that doesn't make sense that it would be multiple cylinders misfiring (P0300) if only one cylinder was misfiring (P0301).

The CEL was blinking which means it's more than one in 200 revolutions, so the catalyst was in danger of overheating (I only drove it 3 miles back home).

I looked up the compression spec for the 3RZFE which is 127psi to 178psi with the delta between any two cylinders not being greater than 14psi.

Too bad you didn't mention what the spec is since I need to check mine!

After I check compression, I'll check the "valve lash" which I've never done.
Looking up the specs for the 3RZFE (2.7L) I see the cold "valve clearance" is
Intake 0.15 to 0.25mm (0.006 to 0.010 inches)
Exhaust 0.25 to 0.35 mm (0.010 to 0.014 inches)

Apparently shims are available in 17 sizes in increments of 0.05mm (0.0020 inches) from 2.50mm (0.0984 inches) to 3.30mm (0.1299 inches).

That's all I could find out though.

Check out Timmy the toolman on YouTube. He and I made a 3RZ valve adjustment video. I have adjusted the valves on mine successfully a few times. 260k

Thanks. I will check that video out where I think it's WONDERFUL people like you help people like me who have never opened up an engine before.

Is there any way to tell, ahead of time, by sound or compression, if the valves "might" need adjusting (before ripping things apart)?

My compression was roughly between about 165 & 175 when I checked the four cylinders.

Is there any clue in the compression numbers for whether valves need checking? Or is it just something you have to check visually, like brakes are?

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I’m not 100% on this, but I think if your compression was low then it means a valve is already burnt and adjusting would not help. Keep valves adjusted to stop that from happening.

This is the video @JZiggy and I made together for adjusting the valve lash on the 3RZ motor.

Thank you for that 3RZ-FE valve clearance video since it looks like after 200K miles I should probably check the valves.

Do you also recommend checking the timing chain?
Do you have a video on the timing chain?
Do people do both at the same time?

I don't mind buying the right tools but I just wonder if this old tool I already have for a motorcycle overhead cam bucket depressor might work?

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