intermittent misfire...
 

hey y’all so my 3rd gen has been having this weird intermittent misfire, but it only happens after the engine has been warmed to operating temperature, shut off, and restarted. after started, the typical misfire symptoms: rpms drop, car shakes pretty bad, bucks and hesitates when trying to accelerate. heres what i have checked so far:

- checked all 6 spark plugs, all work fine, no soot or discoloration
- tested wires and ignition coils, resistance in all 3 coils are good
- checked and cleaned the throttle body
- cleaned MAF sensor
- checked compression, each cylinder was good with 1-2 psi difference between each cylinder
- checked all hoses, no leaks

i have not checked the fuel injectors yet since i have not had much time to get under the hood and remove them. my guess is that it is an injector that is either not working properly or possibly a bad ground but i’d like to know what you guys think. what has me thrown for a loop is the manner in which the misfire happens. when the engine is cold started, it cranks a couple times, starts smooth and runs perfectly fine, drive for about 20-30 min, shut the engine off, come back after a half hour or so, start the engine and boom, misfire mania. i cleared the codes, so the CEL doesnt come on when it happens but the codes are:

P0300: random cylinder misfire
P0301: cylinder 1 misfire
P0304: cylinder 4 misfire

tomorrow i will have some free time so i will pull the injectors, test them and see if that is the culprit.

An injector was my problem when I had those exact symptoms. They will probably test fine when you pull them because they will be cold, unless you maybe warm the truck up first. My theory is something breaks in the circuit when warm, causing the misfire. I had a P0303 I believe and GB remanufactured injectors from rock auto fixed it, but they can be hit or miss I've read. Good luck!

Sounds like a leaking injector(s) to me.

Did you check the primary and secondary sides of the ignition coils? What were your resistance values? I had a similar problem that ended up being a bad ignition coil that resistance tested within specifications.

I'm going to agree with this. Cylinders 1 and 4 share an ignition coil, so my guess is that's going to be your problem.

Swap that coil from cylinder 1 and see if the misfire code moves to another cylinder. I had the same problem and the coil would test within spec when cold but not when hot and the symptom only showed up after driving for like 30 minutes, moving the coil around confirmed my suspicion

A bench test of a spark plug wire is not sufficient. Heat from the engine bay of 150-200 degrees will accentuate damage in the wire that your 60 degree bench test doesn't pick up. Replace the spark plug wires. Same goes with spark plugs, they are cheap so before you drop $100+ on a coil fix the cheaper options first.

i appreciate all of your posts very much. i tested the primary and secondary resistance for the cylinder one ignition coil again and found that while the primary and secondary resistance was within the cold spec (0.70, 9.7) but after driving the vehicle i found that the primary resistance at operating temp was 0.79 and secondary was at 10.8, which is below the specs listed in the FSM. I hadn’t tested the resistance for operating temp prior to this so I was unaware that the resistance was out of spec. I coulda just done what RandyBoBandy suggested and just swapped the coil but I guess I like doing things the hard way lol. swapped in a new oem coil, waited a few hours, started the car back up, drove around, stopped the engine, waited 30 min then restarted the engine and boom, no misfire. i really appreciate all of your guys help!

also trailer park boys is the f***ing best

take the injectors in to a place like Doctor Injector or similar for cleaning. It's like $32 an injector. If the misfires are happening afterwards, then I would do a leakdown test to check the head gasket. I say this because this is EXACTLY the process I did for my misfires. One injector was a little plugged, then the leakdown showed a leak between cylinders 4/6 on the HG. I ended up having thee bad exhaust valves too upon head disassembly. The logical reasoning I was told was the bad injector caused a bad air/fuel mixture which causes the exhaust valves to crack under the increased pressure load, which also screwed up the HG. So...injectors matter!

I have the same exact issue. Its cylinder 4. Ive checked the ignition coil, swapped the spark plug and plug wire. I've got 198K on the engine. Replacing the injectors is not something I can do. If I have my car serviced I'll have them replace all the injectors. But thats big money.

Im trying to find cheap work around. Do you think the ignition coil is broken (as jkoni426 stated) or maybe just clogged? Works fine on cold start ups : )

I just added some lucas injector cleaner but I have little hope, lol. Has anyone used the OTC Fuel Injector Cleaner? The company says its for direct engines. Is the 3.4L on a 3rd Gen direct injection or port? Is there a "connector" to plug this thing into?

https://www.youtube.com/watch?v=blrA4nOY2mc&t=14s

My guess would be that your issue is a fuel injector.
If the issue was an ignition coil, you would have a misfire on cylinders 4 and 1 since the cylinder 1 coil supplies power to the cylinder 4 spark plug using a wire. its called a wasted spark system. i would pull the injectors and clean them or send them off to be rebuilt. doing the injectors on the 5VZ is not a very difficult task, it takes a little while but just take pictures and use separate bags to store bolts for the parts you take off, and always replace the throttle and intake gaskets when you take them off, you don’t want a vacuum leak making your misfire even worse. good luck

It was the fuel injector. I figured Id update this thread in case anyone else stumbles up it. I ended up changing all of them. I plan on keeping my 4Runner for a long time. So to was worth the extra money. Thanks for your insight!!

I have a 1999 4RUNNER SR5 4WD 3.4 V6 WITH AUTO TRANS.

I am not getting my miss resolved. My compression test averaged 198 psi for the 6 cylinders. I replaced all of the wrong type of plugs with denso plugs. replaced the coils and wires. no joy. replaced the injectors. no joy. replaced the maf, and O3 sensors, one of which was dead. no joy.

When the engine warms up from cold a rough, rolling miss develops, and I get "lean on bank 1 sensor 1" which I replaced.

BUT> if I run the engine with the maf sensor unplugged, which at least gives the correct intake air temp, the engine settles into a very smooth and normal sounding idle, with no missing. The problem is that the injectors are wide open and I can't safely run the engine full rich.

I keep looking for clues in the FSM, the WIRING DIAGRAMS, but no good ideas. I am posting this in the Hope that someone somewhere has solved this issue and knows what I should look into next. I would gladly take this to a mechanic, but don't want to run it the ten miles there in the condition it's in.

I've read lots of very similar on all the Toyota forums, but never find detailed steps to pursue at the point this runner is at.

If you've solved this issue, pls message me or post here.

Thanks and Gratitude in advance

Michael sends

I’m having a similar problem. Just bought a 99 with the 3.4. It had a couple bad injectors and the CEL was on steady. I replaced all the injectors and 1 coil pack for 1 and 4. Now the CEL flashes at highway speeds. Around town and under 65 MPH no CEL flash. The code indicates an intermittent misfire. There is no indication of a misfire, the engine doesn’t stumble and purrs like a kitten. All the plugs look beautiful. I’m stumped.

I'm not getting a CEL for any of this. I am thinking it's the A/F Ratio that's getting messed with. There are two sensors on the throttle body that I am going to check out today.

Then I am going to test the wiring to the injectors.

Wiring might be the issue because the truck had rat poop in it, and i found one short lead that needed the insulation taped, so checking for grounded wires might be a solution.

Then I am going to do a leak-down test.

Something is amiss, and I am hoping it is not the head gasket, because that will kill my travel plans.

Hope you find your issue soon, maybe it will fix mine!!

Ciao,
Michael