1999 Toyota 4Runner Limited 4x4, 160,000 miles. This issue became apparent when I encountered a vehicle doing 45mph in a 70 mph zone. I pretty much floored it to get around them and the engine "choked, stuttered, stumbled" until I backed off the gas.

Meanwhile I have performed some long overdue maintenance, not to correct the issue but just a long list of things that needed attention. None of the maintenance has affected the problem.

Replaced timing belt, water pump, tensioner, idler bearings,etc, PS flush, replace TPS, plugs, wires, cleaned throttle body, Mass airflow sensor and IAC valve. Note: all parts replaced with OEM parts, not aftermarket.

I double checked the coils and the wires to make sure each ran to the respective cylinder.

Thinking it could be a bad coil I pulled the spark plug boots one at a time and the engine ran poorly when each was pulled, each produced spark at least an inch away from the plug.

Thinking it may be an injector issue I pulled the three injectors on the passenger side that I could get to and the engine ran poorly... this also threw a bunch of codes that I cleared. Pulling the camshaft sensor produced a code which I cleared. Disconnecting the Mass airflow sensor killed the engine and produced a code which I cleared. The sensors and computer seem to be ok.

The previous owner had problems with the fuel pump and fuel filter, each was replaced twice... that's all I know about the history of this vehicle.

Any ideas and or help would be greatly appreciated.

Sounds like a possible fuel delivery issue. I would def look at the fuel filter and verify its installed the correct direction. You could even just replace that yourself, that way you know for sure its been done.

I'm dealing with a similiar issue right now, but it actually got bad enough that the engine wasn't even idling well. It started as hiccup at 50mph in high gear with the torque converter locked....press on the throttle a tiny bit for a grade and it would stumble. It did that 2-3 times over the period of a week, and then one day it started stumbling almost constantly under any load....and then by the end of that same day it was idling rough. I parked it that night and started taking stuff apart.

Right now I have new plugs, an AirRaid intake tube (I ripped my factory one taking it off) to put on it, and I've taken the Crank Position Sensor out and cleaned it off...it was very oily and grimy due to a front engine oil leak. I'm actually kind of hopefully that it was the crank sensor...meaning I can fix the oil leak and then the problem stays gone. However, I haven't started it back up and tested any of the coils yet etc....so I don't know what I'm going to get.

My injectors were cleaned and tested by Witchhunter about 3 years ago....so it could be an injector, but I don't know yet. It does NOT seem like just one cylinder....which in my troubleshooting is ruling out injectors and coils. Seems more like a TPS or CPS sensor issue now. Again, I don't have any conclusion yet. I'll post back with updates as I work it out.

Measure the primary and secondary coil resistance. It’s highly possible you have a bad coil. Especially if your cat glows red hot like the old CJ did when the coil started going bad.

When a coil starts going bad it will spark lightly loaded. Under higher combustion pressures it will not. It will act like a fuel delivery problem.

I do not like Toyota’s way they detect misfires.


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All great suggestions, thank you... going to google how to test the coils now.

Will report back my findings in a day or two.

Might also be the fuel pressure regulator.
It's mounted to the rear drivers side of the fuel rail, and had a vacuum hose that runs up under the intake plenum to the intake baffle.

Pull the hose from the baffle and sniff. If it smells like fuel, your FPR might be going dying. The little check valve that regulates the fuel pressure might be going out. This will give you some of the same symptoms as a bad fuel pump or filter.

I could easily tell mine had failed; it started puking fuel into the baffle through that vacuum line.

I had a quick CEL PO171 Lean code (I think; it was near 4 years ago) that flashed once, then went away and never came back.
Also, just because you don't have a CEL, it doesn't mean you don't have a pending code. Get yourself an OBDII Bluetooth reader and the TorquePro app.

Ok, so I ordered a coil so I would have a known good test coil. It tested 1 Ohm of resistance, checked all of the other coils which had the exact readings and found one with .7 Ohms resistance and replaced that coil. Engine starts immediately now but the sputter at 3500+/- RPM still exists.

I took some video, may take me a while to figure out how to post it so bear with me.

I have not yet checked the fuel pressure regulator but will do that on Monday or as soon as I can get to it.

Thanks again for all of your help and suggestions!

I replaced all 3 of my ignition coils with Denso 673-1201 (not Toyota branded, but the exact same part for less $$), replaced the plugs, cleaned the MAF, cleaned the crank position sensor, and cleaned the throttle body.

Started it up, and it runs perfectly, stronger than it has in a long time. I started suspecting the coils after I realized my gas mileage had been getting poorer.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Ive been having the same symptoms you mentioned. I've cleaned the MAF and replaced the fuel filter. Next on the list I will do the coil packs as they seem to be original at 277k Thank you for the info.

I had a similar stuttering issue under any sort of heavy acceleration. It felt like transmission slipping, but was actually a misfire. It took about a month of driving before I finally got a CEL code to come on.


I replaced all coils and plugs and that fixed it. They had never been replaced, and had well over 220k on them at the time, so they were due to be replaced.