Hi All,

Been lurking these forums since I bought my 4Runner in January. I've come across some misfire issues and have yet to find a remedy.

The vehicle is a 2000 4R Limited with 4WD and Rear Locker.

On initial cold start, it runs great, no issues whatsoever, no codes, no lights, no indication of any problem.
The problem however arises when I drive it and park it for let's say 20-30 mins. I would start it again and would get shaking after about a minute. When this happens, it seems to go into limp mode and I cannot go past 1500rpm. Sometimes I'll get a code (P0300, P0301, P0303, P0305, P0306). Most times, it'll just show a pending code. If I give it a couple revs, it'll usually fix it and it'll drive just fine again or if I turn it off and start it back up, it's fine. If I drive it and park it overnight and start it again, I have zero issues. Seems to happen only after it sits for 30-45 min and I drive it again.

Here is all that I have replaced with new OEM Toyota parts: TPS, MAF, spark plugs, crank position sensor, and air filter.
My mechanic, as well as another friend who ran into a similar issue, but only on cold start told me that it may be early signs of a failing head gasket. Sounded like coolant may have been seeping into the cylinder and causing the shaking until the excess coolant was burned off. At this point, I had run out of options. I went ahead and did the head gasket as well as other misc things that needed to get done anyways. Head gasket work was done along with a new knock sensor harness since mine was old and brittle, spark plug wires, coil packs (only OEM Denso).

However...$3k later with all these new parts, machining the heads, reseating the valves with new seals, new OEM injectors, and a new fuel filter...I'm still running into the same misfiring issues. It's also worth noting that the engine was replaced at some point as the VIN plate was from a different 4runner.
Any ideas what it could be? There was an issue with the throttle body sticking. If the throttle body is forced closed, the motor will begin to shake like it's misfiring. I also don't know if the fuel pump was ever changed, so I'm not sure if maybe the motor is bogging from a failing pump not supplying enough fuel to the injectors. The other concern was that because of how old the car is, the harness for the fuel injectors may be brittle so we may need to finagle with it. Aside from those 3 things...I am completely lost. Any help would be greatly appreciated.

Might be time 'for motor west injectors.

Could be an injector as they are a common problem after a few decades, and possibly wiring, or missing teeth on the crank sensor trigger ring, not sure if a bad cam sensor would cause this?

Like the others said when mine had those symptoms it was a bad fuel injector on cylinder 3 (P0303).

I have a similar issue.

Replaced all plugs, coils, and injectors.

Smoke test shows no vacuum leaks.

Every part I replace makes it worse.

Chasing ghosts is always a good time.

I'm assuming the spark plug wires were replaced. Are they routed properly? There is a specific order in where to cross them.

Has actual spark been verified?

Next, is even though you have a new head gasket and all, what are the compression test numbers for all the cylinders?

Sorry to hijack this thread but I'm having similar issues. Recently purchased 1999 Limited with 271K miles. Started having rough idling and got codes P0300, P0304, and P0305. With unknown prior maintaince, I put in new denso plugs and wires and did a seafoam spray treatment. Runs great when cold but has issues upon warm restart. Compression test shows 170-180psi in all cylinders. Would new injectors be the next logical step? Thank you for any suggestions.

It is likely they get heat soaked and stop functioning. The injectors should be 13.8 ohms give or take a couple when cold. Replace them if they Re out of spec.

Thank you. I'll get some injectors ordered and installed.

Misfire codes are either a fuel, air or spark issue. You've handled the spark maintenance items. The other issue could be air that isn't metered correctly. Try cleaning off the MAF with loads of MAF cleaner/carb cleaner and see if that helps the stumble and misfire. Also change your air filter 1x per year.

The last would be fuel delivery which is controlled by the front O2 sensor and our friend once again, the MAF sensor. It could also be the injectors but if you haven't ordered them already, put 1-2 bottles of high quality injector cleaner such as Lucas, Royal Purple, AMSOIL. Avoid bargain brand stuff. If there's any improvement, even slight improvement, it may be the injectors causing the misfire. Instead of replacing them, send them off to an injector cleaning service as it'll only cost about $125 for the service + shipping. You might even find a local place like I did and have no shipping costs.

Should have mentioned that I've cleaned the MAF sensor and run injector cleaner through it with no improvement. Air filter is good. I'll most likely order injectors from Motorwest as mine have 270K+ miles on them. No local shops in my very rural area. Thank you.

The current codes are: P0300, P0303, P0302, P0171. No codes for any failed sensors, like O2, MAF, etc.

I have a hard time with this because the 220k service encompassed so many parts... how can I possibly know what was disturbed during the maintenance?

All new wires along with the other parts. I can't see how it's possible to route the wires any way other than one.

Why would compression be an indicator when cold running is perfect? Outside of this suggestion, I've tried everything I've read and been told on these forums with no luck, and I just can't keep trying stuff with no understanding of the logic.

I've also tried the local "Toyota Specialists" - at $900 for an injector cleaning and one replacement. No improvement though, just a suggestion to replace my brakes and suspension, and a suspicious vacuum line plugged with a rubber cap? Thanks.

Is the factory manual is an accurate troubleshooting guide?

Or, is taking it to my nearest Toyota dealer a sure-fire solution? I'm at the end of my patience for solving this puzzle. If I don't find an answer soon, I will incinerate the truck and the haunted demons that possess it and accept that 4Runners just aren't as reliable as 'they say'.

Wouldn't the ECU throw codes if the O2 or MAF sensors were dirty/bad?

The other factor for a hot restart issue is a bad head gasket.


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Finally had time to replace the injectors yesterday. Runs great now and no more codes after the first couple of drives.