Archer1968

Please help!
I have a 1999 Toyota 4 Runner 3.4 Liter Engine (the 5V Engine) with over 208K miles on it.

About 6 months ago it would very periodically misfire under acceleration (loss of power and the engine would rapidly jerk for a very brief period (a few seconds). The problem has progressively become worse with now some new issues that have come about.

At first, when the 4 Runner is cold, I can start it up and it would drive fine for about 10 to 15 miles or until I shut it off and then a few minutes later, would start it up. The engine will run very rough and with the ODB-2 reader, I get a P0304 error (Misfire on cylinder 3). This too has become more and more frequent.

Now, the misfire seems to start soon after the 10 to 15 miles and seems to occur right after I hear a strange “Chirp” and will continue to misfire until the engine completely cools off again.

The problems still persist, but I am idling at 1500 RPMS at normal temps and when I am driving anywhere between 30 to 60 miles per hour, the vehicle feels like it momentarily stalls out- the RPMS drop 300 to 400 RPMS for a second and then picks back up again. This occurs about every ˝ mile. As always, after 10 to 15 miles or after it gets warmed up good, the misfire comes back on cylinder 3.

I have not taken it to a shop yet due to the prices and have not sat idly by. I have exhausted myself with trying to fix it back up.

I started with changing out a relatively new spark plug wire set and spark plugs (duel prong as recommended Denso Double Platinum) replaced and swapped around the coil packs and checked and cleaned a relatively new EGR Valve. The problem still grew progressively worse. (Twice on the wiring and three times on the plugs) Dielectric greased on all connectors!

I then went to cleaning and replacing the fuel injectors (cylinder 3 replaced and have also swapped all of them around with all new gaskets). I checked the Fuel Injectors with a long screw driver and listened for the clicking. All is good and no fuel leakage and no discernable air leakage.

I pulled off and cleaned the throttle body, replaced the gasket and cleaned the Intake Air Control (IAC), replaced the Throttle Position Sensor (TPS) and replaced the Air Plentum gaskets (Upper and Lower) and the Mass Air Flow Sensor (MAF) has been cleaned with MAF safe cleaner.

None of this helped.

Further I have checked and cleaned the Air Resonisance chamber and checked as best as I can for vacuum leaks and repaired/ replaced vacuum lines.
I have run two cans of Seafoam through the engine and replaced the fuel pump and fuel filter and checked and cleaned the Cam Shaft Position Sensor.

Still no results on the symptoms as described above.

The exhaust is not smoking (clear exhaust fumes), no antifreeze in the oil or vise versa and the temp is with in normal ranges. The spark plugs show a little blackness, but more on a normal side than anything.

The only things I have not done are check/ replace the timing belt- still not due for a new one.

I have not checked the crank shaft sensors, EGR Valve or the Fuel Pressure Regulator.

What else can I check/ repair?


Thank you for any insights or help!

roland750

I recently had a similar problem and it turned out to be a fuel injector. One other option is swap around the coil packs and see if your codes moves. Not likely but worth a shot.

MaK92-4RnR

Its your fuel injector. Try swapping your coil packs ( they're all the same and all 3 are located on your passenger side ) if this doesn't solve anything. I'd change your fuel filter, see if that helps. if still nothing. Its an injector being stubborn.

I did this on my Cousin's 97 4Runner and hers has been problem free. we only changed the single injector that was throwing the code, and its been great since. She's at 214k miles now.

Archer1968

Thanks for the insight. I have swapped injectors around, but who knows. I will try it again. A friend also suggested to unplug the connector on the fuel injector when it is misfiring and see if it continues or quits.

Just_Me69

Have you tried checking cylinder four? The one that the code is for.