I've been dealing with an intermittent misfire for the past month that has been gradually getting worse and worse. It started out misfiring at lower rpm's and higher load (think highway speeds going up a slight grade). At first I thought it might have been torque converter shudder but as it got worse it would eventually do it in all gears sometimes even just idling. I've been using a 2000 FSM to help diagnose my problems. Misfire is rhythmic which leads me to believe it's 1 cylinder misfiring. No current or pending DTC's.

Helpful info: 2000 4Runner Limited 4WD 3.4 216xxx miles
-Fuel filter replaced w/OEM in March 2019
-Tried different set of known good spark plugs with no change
-injectors changed 15 miles ago with remanufactured injectors from LC Engineering 5VZ (V6) Equalized Fuel Injector Set (99-04) New injectors 13.9 ohms resistance at 80 degrees fahrenheit.
-plugs/wires changed 800 miles ago when valve cover gaskets were done.
-removed plugs and verified clean and properly gapped (new OEM dual electrode)
-Resistance checked spark plug wires (new OEM wires)
-Resistance checked ignition coil boots 1.2 to 1.3 ohms no rips or tears
-Resistance checked coil packs while hot and cold
HOT: #1=1.2 ohms primary/14.7K ohms secondary
#2=1.3 ohms primary/14.31K ohms secondary
#3=1.2 ohms primary/14.34K ohms secondary
COLD: #1=1.1 ohms primary/13k ohms secondary
#2=1.2 ohms primary/12.67K ohms secondary
#3=1.1 ohms primary/12.72K ohms secondary
-Verified voltage at ignition coil packs. All coil packs had 12.17V with battery/source voltage at 12.26V. (Key had been on for a while so I'm not concerned with the lower battery voltage. Vehicle shows 13.8-14.4V while engine running.)
-Resistance checked camshaft position sensor (hot): 1374 ohms
-Resistance checked crankshaft position sensor (hot): 2437 ohms
-Resistance checked MAF: 1354 ohms @ 90 degrees fahrenheit
-Resistance checked TPS: 496 ohms closed and 2673 ohms open.
-Resistance checked ECM to Igniter T9 wiring: 0.4 ohms
-Resistance checked Igniter to Ignition Coil wiring:
T1 to Coil #3=0.2 ohms
T2 to Coil #2=0.3 ohms
T10 to Coil #1=o.3 ohms
-Compression tested 190-210 psi on all cylinders
-No noticeable coolant loss
-No vacuum leaks found. Used Carb cleaner spray method.

Any helpful insights or additional things to check would be greatly appreciated.

Timing? Compression/leak down test? Losing any coolant?

Wow.. you checked everything really good Bad luck. Since the CEL isnt recording it. I look on the non electrical side of things.

Just some thoughts:

Check the Fuel pressure at the rail and make sure your Fuel Filter isn't clogged and your pump is able to provide proper fuel pressure to your injectors.

Check for vacuum leaks.. We get enough of a leak on the vacuum can cause rough idle and possible misfires as letting too much oxygen in.



As you explained your issue it slowly started showing up and getting progressively worse. Makes me think that something is plugging or a manifold leak is getting worse.

An EGR Value issue would give you crappy idle and poor performance but I don't think it would cause a misfire but worth verifying the its working properly.

PCV Value would be rough idle and stull if stuck open. So doubt its the valve causing the issue with the misfire.

How bad of a misfire we talking here?? Do you notice it more when its cold engine or hot engine?

You think your loosing a few cylinders all the time or intermittently misfiring?

Compression was 190-210 on all cylinders and no coolant loss. Timing belt/water pump was done in March around 3k miles ago. No coolant loss.

Thanks for the compliment! I try to give as much info as I can when I have an issue like this.

I don’t know how to check the fuel pressure at the rail without the special service tool that Toyota has that goes between the return fuel pressure regulator and the rail. Fuel filter was replaced with OEM in March.

I was hoping it was a vacuum leak, but 3 cans of carb cleaner later it didn’t sputter at all. Short term fuel trims are around 0% +/- 4% with long term fuel trim between 2-3%.

I don’t think it’s PCV or EGR (do we have an EGR?) because it idles pretty good until the misfire gets worse. It started out as a hot engine misfire and has progressively made its way to starting out colder and colder. It’s a very rhythmic misfire so it makes me think only 1 cylinder. When it’s at operating temperature I can give it just the right amount throttle under load to make it a dead miss. (Or at least it feels like a dead miss.)

We probably don't have an EGR I was just going through a list in my head.
{hard to find an EGR no EGR on any OBDII 3.4L V6. } Sorry that's my bad.

When was the last time you changed the fuel filter??

Ah the old carb cleaner vacuum leak test...Yup.. That mostly finds them..

This is a tough one. I would think if one of your sensors were flaking and error would be detected.

All the wiring good on the engine? Any insulation rubbed through. Maybe it is just a coil not firing from wiring intermittently shorting. If its rhythmic we have a pattern and a pattern can be found.

Fuel filter was replaced in March with oem. I haven’t had a vacuum leak I couldn’t find with carb cleaner yet. I didn’t think we had an EGR but I wasn’t sure. I was thinking it’s heat related that’s why I tried doing my testing with it hot. I thoroughly inspected the injector wiring when I replaced the injectors last weekend and didn’t find anything visibly wrong. I have a Chinese pirated version of Toyota tech stream but it’s been glitchy and freezing before I can get it to show misfires. I’ll try uninstall/reinstall tomorrow and hopefully be able to see some data

If heat related, possible intermittent sensor acting up. Still passing the basic diagnostics and hiccuping.

This is one of those things that will drive you nuts to you solve it.

I wonder if the actual toyota scanner and software would see anything different. I doubt it though.

I am running out of thoughts quickly. As it seems everything is checking out as fine.



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Are you getting any pending codes? When mine was misfiring I only got a CEL once going up a hill, but would show a pending P0300 & P0303 other times it happened.

I'm running out of ideas as well. I think I'll try replacing the #1 coil pack. It's testing within specifications, but it is consistently higher resistance than the other two both hot and cold. I ordered a denso off amazon for $60 and it'll be here Thursday.

No codes. Pending or otherwise.

I would go over the plugs and wires again. I know they are not old and test fine but once a cylinder starts to misfire that plug is usually toast. It happened on my 97, had a misfire, no codes so I changed the plugs out again even though they were relatively new and I have not had any trouble since

Plugs are clean and wires test well below the 25k ohm per FSM

{I actually had the PO never change the plug sand the electrode broke off. It would misfire but through the Check engine light. Plugs had 210K on them. Gee I wonder why the electrode failed. I have a picture of that plug somewhere. }

Anyways. I was wondering if it was simply a bad plug even though its new misfiring? Would explain the no codes and the coil is firing.. Possible bad coil too even though its testing good. Excellent thought on the coil pack, as you can use it as a reference to check the other 2 coils..

I am sure you did the wait till its dark and mist the engine compartment looking for an arch test. Would verify your wires not arching which I doubt they are.

We are getting into the side of things now. :-(

Threw a known good set of spark plugs in and misfire continued so I put the newer plugs back in. I actually did mist the wires with salt water mixture to see if I got any arching with no luck. I agree that we're in the realm of wtf now lol I can't believe how terrible Toyota's misfire code requirements are... I'm really hoping the ignition coil is the issue. This is the last "dart" I can afford to throw at this thing for a couple paychecks