I've researched time and time again, and I've read some solutions, although they are not fixing the problem!!

Story: I have a 1999 4Runner Sport V6 3.4 with 170k+ on the original motor. A few months back my truck started to misfire on my way home around 60mph, almost out of nowhere because I didnt feel anything before reaching my destination. I did a complete oil and radiator flush, and even replaced the o2 sensor behind the CAT as per instruction by my tech. That didn't solve the problem, and the CEL was still lit. CEL was showing that cylinder 1 and 3 were misfiring. Techs cleaned out the MAF for me, and recently I sent my injectors to RC Engineering to have all 6 injectors cleaned. I even replaced the fuel filter with a brand new one. I was sure that this would fix the problem. Nope. (I replaced spark plugs around 150k miles, and they spark just fine when we tested them last month)

Truck was running fine up until yesterday which is about 5 days after installing new filter and rebuilt injectors. Misfired while going home last night, and again this morning. Usually it misfires anywhere around 70-80+miles per hour. Especially when going uphill around 70mph.

I checked my coolant before heading out this morning, and I am not losing any coolant. I've been checking it randomly, and it always seems to be at the same spot when the engine is cold, havent checked while hot. I also checked the oil dipstick, and it doesnt look milky. Oil is perfectly clear.

So I'm thinking it cant be the headgasket, because all the stories I've read regarding the headgasket the owners have lost a considerable amount of coolant, and their oil starts to turn milky or different shade of color.

My CEL codes are reading P1135 and P1130. Now I hear this either has to do with the MAF, A/F, or O2 sensor. I have no problem replacing any of these sensors, but I'm wondering if this may be the cause of the misfiring? The last thing I want to do is have to replace the headgasket as that will hurt me financially. I am planning to sell the truck soon to pick up something newer, but don't want to leave the new owner with problems. Although if it really is the headgasket I will just have to sell the truck as is, and notify the new owner of the problems. Any help would be greatly appreciated. I hope I've given enough information regarding my problem!!

EDIT: btw, I will be checking the coil packs today to see if maybe that's causing the problem.

 

the codes are for front air fuel sensor. replace it.
if your only codes are p113x series, that is all you have to do
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are you getting misfire codes ? (p0300 series)

a bad a/f can throw too much fuel (runs rich because sensor thinks
--too lean, send more--) and that may cause misfire

 

Thank you for your reply! No other codes so far, not even misfire notifications. Would you happen to know the part number to that a/f sensor? Or should I just search for a front a/f sensor?

 

Nevermind, I had my rep at the Toyota dealership help me find the part...I'm picking it up today, and will install it. Let's hope this fixes my problem!!

 

Good call bigballs, I have had the same prob and done a couple write ups about it. It can be a frustrating problem fo sho!! Good luck, hope it fixes it, dude!!

 

Im kinda dealing with the same situation but only 1 cylinder(#2),changed the plugs/wires and am 90% of the way through the 200,000 (228 and change on the truck)mile services when this started.I dont have the code as my device just says (from what i recall)misfire on #2.Its driving me crazy and im down to thinking its a fuel injector(they are all i have left to do as far as service)but the miss is getting pretty bad,plug looks good and spark is good so would i be correct in thinking the injector is going?Or could it be the A/F going or gone bad?would this cause it to miss on a single cylinder

 

update please did that seem to fix it ?

 

I was wondering the same,Found out after a closer look at my codes it is misfiring on 3 (1,2,3)cylinders but im thinking coils for me.

 

ok so here's my update.

I swapped out the A/F sensor bank 1....it stopped the CEL from coming on, but I'm still misfiring. I pushed the truck so it would show the CEL blink the other day which it did. I scanned and I received PO300, 301, and 306 codes. I bought a brand new coil pack for cylinder one, and bought new plug wires. The spark plugs were changed out last year, and shouldnt have gone bad. I just plugged in a new PCV valve, and cleaned the throttle body (although I'm going to clean it more this weekend). I'll probably reset the ECU too via fuse.

Still have misfiring issues. I'm somewhat narrowing it down to it being a valve problem now. No overheating, no loss of coolant, no oil leaks or milky looking oil, so it's not the headgasket. I've got fresh fuel going through rebuilt injectors and filter, I've got fresh air via a new air filter and PCV valve to relieve blowby gas. And my spark should be just fine, unless one of the other coil packs or spark plugs have gone bad....still trying to figure out this very frustrating problem. Will update once I find out what's wrong, but if anyone else has any ideas...please share. I was thinking of Seafoaming the motor, but now that I have new injectors, plugs, A/F sensor, etc. I dont want to clog those new items up.

 

btw this what my rig looks like for kicks and giggles

 

update:

Ran some seafoam in the pcv valve vacuum line, oil, and fuel tank earlier today...smoked a bit, not as much as others I've seen. Just went to get some gas, and on my way back to the office the misfire CEL went off again. This time I was on flat ground, no incline, and I wasn't pushing the truck that hard. CEL went off at 60mph but only blinked. Checked the code and received a PO301. Cylinder 1 misfire. I already installed new plug wires and a new coil pack on cylinder one. No more misfire code for cylinder six (which is great! and it probably was because of a bad plug wire). Will drive the truck home tonight and see if I get the po301 again. If I do, I'll grab a set of spark plugs and install them after my oil change this weekend, since I seafoamed my motor it's necessary anyway. I'll update after to see if this could potentially be the resolution. If not, there's something mechanical going wrong internally, or the timing belt is off.

 

Bump...

What was the resolution (if any) to this issue? I just got P0301 and P0171 codes yesterday and have started troubleshooting... plugs changed, MAF cleaned, coil pack swapped and injector resistance/supply voltage checked so far. My suspicion is still the injector, but I would like to know what solved yours.

 

OK Mickwheeler, I am buzzed and this thread is slightly old(I love Jim Beam).....let's see if we can get you straightened out here. It still could be an injector, even though they rarely fail, I keep an extra one on hand. But if you have swapped everything out, IE coil packs, injectors, etc with no avail then you are still on the right track. Did you take the upper intake manifold apart in order to access the injectors, packs etc? (let me see if I can find a pic)..ok, just made a pic, I'll attach it!! ANYWAY.......Some ppl swap work on stuff without taking the intake apart at this area, some ppl do....I chose to pull the vac. lines apart, throttle cables etc to get better access to the fuel injectors(FI'S)since my hands aren't small. There IS a coolant line going thru the upper intake so pay attn to what you're taking apart, as well pay attn to coolant flying everywhere and ultimately pissing you off!! Be sure to re-attach them in the correct fashion. The plenum gasket seems to deteriorate over the years, which may lead to the "sucking of air" from the outside of the manifold which=baddd!! Mine had a powder-looking-substance when I removed the upper intake manifold, which was probably the gasket that had degraded over time. Replace that daggum gasket, it is only like some $14 at the stealership, but may save your ass. Even if you're not all-up-in-there working on stuff, pull it apart and replace it, it can't hurt. Clean the area really good before replacing gasket and torquing down. As always, check & triple check your vac lines, throttle cables, bracket's etc before starting/driving. It has been a long time since I posted on this subject, so hopefully this helps!! Let us know!!

 

Thanks for the quick reply... I had not considered pulling the plenum or replacing the gasket because my problems were all on cylinder 1.

In other news, I cleaned the MAF and now have no more P0171 (system too lean) code, but still have the P0301 (misfire cylinder 1) code. I swapped the coil pack to the cylinder 5 position and the misfire stayed at cylinder 1, so that eliminates the coil. I then unplugged the cylinder 1 injector (at idle) with no discernible difference... so I'm going to swap the injector tomorrow and cross my fingers.

Further, I'm going to take your advice and swap the gasket... it's cheap insurance.

As for the timing of this issue, it's ironic. I picked up a long block this weekend to rebuild... so I'll have to fix this or risk transplanting it to the new engine.


Thanks again, I'll post the solution... whatever it turns out to be.

 

No problem, bud......and might I say WOWEE, you already got a long block for rebuild/replacement?? Just give it a little more time/research before transplanting. These type of problems can be frustrating, but are usually an easy fix by using process of elimination, like you have been doing!! As you might have seen, these crazy 3.4 problems/trouble codes can seem to be other problems when in fact they're not. As long as the motor has not been ragged or the fluids neglected, normally it's not a valve or compression problem. How many miles on her? She is a nice looking 4runner BTW, what lift do you have, I see 2.5"? But anyway, I had emergency surgery thurs, and I am slightly jacked so I'll try to stop rambling. Pop the intake off real quick to investigate, that gasket could very well be the problem. If you are hard up for a FI let me know. I went to the local stealership, talked to some of the mechanics there, and asked who had an extra FI laying around in their toolbox. The long-time yota guys keep ˟˟˟˟ like that laying around, I gave him $20 for one, popped it in and worked fine. But, upon further investigation found it was the plenum anyway. I am looking fwd to your comments/solution. Just stay cool and don't rush to judgement, like swapping motors unless you're 210% sure!!

 

First, this is the place to ramble. If not here, then where? Second... surgery? I wish you a speedy recovery. Third, thanks for the kind words. I got addicted almost immediately after buying my rig... it's my first Toyota and I'm definitely hooked.

As for the long block and engine swap, it was in my plan from the beginning. My rig had 170K on it when I bought it and has 270K now. I replaced the transmission the first month (broken 1st gear shift fork when I got it) and knew the engine would eventually need a transplant as well. So I'm 210% sure that it's getting swapped... It's just that I had hoped to do it without having to to nurse the current engine while I completed the rebuild.

I'm going to pop the plenum and cylinder 1 injector tomorrow and continue the diagnosis, I'll post the results.

 

I just realized I didn't answer your question as to what lift I have... it's Performance Parts springs over Bilsteins. They aren't the best springs (by far) for off road, but they are great for the 80% road 20% trail that I do.

 

Nice, we'll try not to hijack the thread on lifts and so forth, we can pm on that. I didnt realize you had so many miles on that 2000, dang. Well, if a long-block is in order, then that's what it is. Let us all know on the gasket ordeal. Thanks for the speedy recovery thing!

 

Follow-up... I didn't pull the plenum gasket yesterday, but I did pull the (1, 3, 5) injectors. After cleaning and testing them (good resistance and flow), I put on new o-rings and reinstalled them. No change, still a misfire on cylinder one.

I also noticed a faint chirp or hiss when I started it up... Which leads me down the path of plenum gasket or (big sigh) head gasket.

My next step will be to spray carb cleaner around the intake to find out if it's a suction problem (vapor pulled in). Failing a positive result, I will be using a stethoscope or hose to check for expulsion of gas around the head/cylinder. Fingers crossed for the plenum gasket.

For giggles, I called a Toyota guru in Florida and picked his brain. Other possibilities include valve lash out of tolerance (unlikely), stuck valve (possible at 270k) or displaced/stuck valve shim.

I'm forced to drive it at the moment, so I will commence the rebuild on the replacement post-haste.

Thanks to all those that have posted their experiences, this forum is an invaluable resource.

 

Cool, hows it going? checked anything yet?