I am posting this to help people who have rough idle issues.

Alright. I have a '98 4-cyl.(2.7L 3RZ-FE) 4runner.

BACKGROUND
I bought this 4runner from the first owner. it had 180,000 miles in it for 3,500 and boy did it run smooth. Before this, we used to have a the same '98 4-cyl. model until it rolled over which was totaled(no injuries whatsoever). So when I bought this 4Runner I knew almost all the specs and how to do all the maintenance when I bough it.

When I bough it, all I basically did was change out all oils(engine.trans.diff) and the front brakes(rotors,pads). Also noticed that the manifold had a hairline crack between the back two cylinders and the front two cylinders.

PROBLEMS
Around this time last year, my 4runner began to rough idle. It started gently and got progressively worse. By now I had 230,000 miles on it and there was dozens of things that might be wrong with it. After a week of rough idling, the check engine light went off. OBD2 reader said misfire, not good. I ran my car for another week and the light turned off. The only thing that I had ever changed was pumping gas at another station. So I changed my gas and began to pump premium which I though was the solution.

SEAFOAM
2 months pass and then I get the check engine light again, my car also began to rough idle even more. Ran a can of seafoam and the engine felt a bit more stable but not 100%. I though that the one or more injector(s) might be dirty or clogged. I ran it through 2 more tanks with seafoam just to make sure and it continued to rough idle. So Sea foam and dirty injectors where not the problem or solution for me.

NEW WIREING
So my next best guess was sparkplugs and wires. Checked my plugs, all good but I decided to buy a new set anyways while I was at it I spend an extra 40 on a new spark-wire set. got it installed. turned on the engine, more HP but it still rough idled.

DEALER
My last resort was to get it checked out at the dealer and ask for a check-up. By now, more than 200k miles it was running really rough. I got 17mpg or so(normally 22-25)because almost all my commutes and roads/highways are 50-70mph in my area. My check engine was always solid an would blink on any take off or even cruising on the highway. I gradually did not catch that my HP was slowly decreasing. Had a chat with my dad and we decided to take it to the dealer. ran me $90. Diagnosis: low compression on Cylinder 1. Claimed that my valves where bad. their solution was a top end job which ran me min. $1500 for labor, plus all parts which they claimed would be another $800(new valves and gaskets). They also suggested we could find a new engine and swap. that would run me the same $2500. My belief at this point was, the darn manifold might have screwed my engine up.

My Solution:
I continued to use it but only if necessary. I wasn't too happy so I decided to do the job myself. researched this forum. Found the repair book for the same engine from a Taco. bough my valves ($7 ea.) at a CARQUEST (yeah they still exist haha) bought my whole engine gasket kit on Amazon(Fel-Pro). Bought my new Manifold $90(Amazon) just in case I got it running smooth again ill slap the new one in there. Total cost was about $280 with a couple of cleaning sprays.

WORK
Took out all the intake, wires, engine cap, injectors, manifold. then I loosened out the distributor from the top block and laid it out on the side, same with the power steering canister and pump. Disconnected the timing chain after setting the engine in the "zero" position and took out the valve rods I guess you may call. Took out the main 10 bolts(hard as he11) to finally take off the top block. put my "valve rods" back on and flipped it upside down. 1 darn valve was worn out and looked like an oval. Whole thing was muddy. I took the block to a shop to get the bottom of it resurfaced, replace the valves, the block cleaned, and the valve shims rebalanced. That cost me another $100. When I got it back it was like new!! the guy told me all the other valves where perfect and where not replaced.

That all took him one day, got it the next morning. Meanwhile, I cleaned the cylinder heads which had this black tar/carbon which was really hard to remove. I cleaned my injectors, ran some carb-cleaner through my intake. I also took out my alternator and literally dipped it in engine degreaser(good as new!).

ASSEMBLY.
Long, long story short. put it back all together with new gaskets. had my dad take a look at it when I was done. fired it up. for 30 seconds, engine was stable but a lot of smoke was coming off. My new manifold did not sit properly into the exhaust(back not the block). took it off. slept on it. took the old manifold to an shop where they weld and they wend the hairline with bronze. cost me $40, I put it back in. sat properly. turned on the engine, second rev. after a small rev. no more lights!!!
rev'd the engine. strong and responsive. I left it on for 20 min or so, while I cleaned up my tools ready for a joy ride.

I got her done!!! I have added like 2k miles since, no more check engine lights, misfires, hick-ups, rough-idles. My MPG jumped up to 25ish. I feel like I have a new car haha. I returned my new manifold. I basically did this $2500 job with $320 or so. I'm about to change my oil again. I wanted to thank people on this forum for providing links, ideas, files and pictures(that's why I joined). and If you have questions, I'll try to answer to the best of my knowledge. Ill try to add more pictures to my albums so you can see it. Its the gray one I rebuilt.

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Damn! nice work. Thats the beauty of DIY- save yourself sooooo much money. Glad to see its up and running properly

So you knew the manifold was bad but did nothing about it? Couldn't this have been avoided by changing out the manifold when you saw the crack?

@T4R2014
Possibly. There's a huge doubt in my mind that the valve was almost shred to pieces because of that. There are some routes that I am forced to take home where I'm at a 25 degree angle for 1/4 of a mile. So pushing the engine everyday may also be a cause. Dude it had more than 180,000 miles on it, what else do you expect.

Also, the purpose for my post was to help people with idling problems and providing a troubleshooting list.
Like:
SeaFoam(dirty injectors/dirty tank)
premium gas(bad gas station)
spark plugs and wires
compression test

other tests that I did not include were:
diff/new battery
O2 sensor
air filter
and others I cant think of.

Atta Boy! When I get real big, I'm wanna be just like you.

It's a strong possibility. Which valve was bad?

Hey man good for you! If it helps any I have the LC header and I can say for the cost it is very well made and mated perfectly if you are looking for an aftermarket solution.

I think that cracked manifold toasted the crap outta your valve personally. I did my headers and I had a small crack developing and when I did my valves shims next I noticed the clearances on the exhaust side were pretty much all off.

Nice write-up, but if I can quote many a wise man...



Glad you got it fixed, and that sounds like a fun project. Always good when you can make such big improvement for not alot of green.

It was actually an intake valve that was bad. Cyl1 towards the back. So it was not the one on the edge but the next one. It's a 16 valve engine if you can recall. It looked like an oval and the surface was really bad. So I really don't understand why a small hairline on the manifold could have caused that but who knows I might be wrong. Heat differences might have been the issue. Also, I just changed the oil. Running great and it turns on in an instant!

After reading this thread, I've figured out you had a cracked EXHAUST manifold. I don't see that causing your burnt valve. Ever.

Your intake valve might have been bad, but my guess is that the hairline crack in the exhaust manifold was allowing air into the exhaust. Since the exhaust gas had more oxygen in it (due to the crack) the O2 sensor detected a lean mixture and added more gas. This caused the engine to run rich (except at WOT) and rough, and triggered the code. My guess is that the cracked manifold was probably your main problem all along.

Here's another thread about pretty much the same thing: Cracked exhaust manifold question?

Might not be a good place to ask this, but I think I knocked the timing off on my 3rz when I was changing the flexplate. I rotated the crank counter-clockwise not knowing that it was a no-no. Is there an easier way to get the timing corrected without removing the timing cover?

It's a 98 4runner, 2.7L auto, RWD. Turns over and runs rough for a second/smokes before it stops.

What is this thing with exhaust manifold causing burned valves?

I'd say most older cars are leaking to some degree somewhere in the exhaust manifold, be it the gasket or a crack.

There is positive pressure in the manifold, I don't know how it would let oxygen get to the valve of the o2 sensor. The most it would do is cause a slow response.

And the vehicle running richer due to more oxygen (if that was possible) hitting the o2 sensor, the cylinder would run colder, not hotter. Running lean will cause an overheat. You run rich everytime you start your car, and every time your are wide open throttling, and you don'T burn valves WOT on that long stretch or road.

Exhaust comes in pulses, with positive and negative pressure waves when you are close to the head/valves. Fresh air can get sucked into the exhaust with any cracks before the O2 sensor, causing running problems.

As for burning valves... I wouldn't worry about that from a cracked exhaust manifold. That's more of a completely open exhaust thing (no manifold at all).

-Charlie

More than likely a valve adjust issue or lack thereof previously.