Greetings! New member here. This is a great site, I've learned a lot about these vehicles so far and am excited to learn more.

I Recently bought a '99 SR5, 3.4L, that has about 120K on it. Within the last 500 miles or so, I did a lot of typical 'new owner PM stuff' - NGK plugs, NGK wires, air filter, cleaned MAF, cleaned throttle body, changed key fluids (rear diff, t-case-front diff, coolant), ran Seafoam through PCV valve, oil change, etc (obviously did the seafoam first, then the new plugs/oil change after...)

I'm pretty comfortable mechanically, having done TBelts, Clutches and the typical suspension stuff on a variety of cars: MKII VW's, E30 BMW's and 4G63turbo DSMs and am also very familiar w/US 'iron' too- 5.0 V8 Fords and 3.1L GM's.

My issue is that I am getting a misfire, but no CEL, which seems pretty strange to me. The symptoms started all of a sudden, yet the car starts/idles perfectly. Symtpoms are: When I get on the gas pedal, or have it in gear (it's a 5spd...), it is very hard to keep running/moving.

I have to practically floor it, just to get it to sluggishly accelerate and even then, it's erratic and 'jerky'. Sometimes it will 'catch' and 'take off', only to bog down and then start lurching/choking again.

After driving even a short distance (which is a challenge!), the exhaust system underneath is super hot, like it's running lean. There's no 'rich'/fuel smell or black smoke. (No smoke at all for that matter and no loss of coolant, so I don't think it's a head gasket...)

The catalytic converter does not 'rattle' or smell bad and exhaust is getting through to tailpipe, so it is not likely a back-pressure/Cat/exhaust leak issue.

I understand as a newbie, the 'search function' is my best friend and I have done a couple hours of research on here and am thinking it is most likely an injector(?) or coil pack. (Maybe my own doing, from using the seafoam??)

Problem is, I'm kind of tight on funds right now and I don't want to throw a bunch of money/parts at it.

Do you think this is something I could fix by running some injector cleaner/doing a fuel filter replacement? (I did run the tank pretty low, right before the symptoms started...).

I hate to buy new coil pack, plugs, wires (since they were just done and are name-brand/correct part #'s for vehicle, bought at Napa, doubt they're bad). Plus, O2 sensors are not cheap and neither are Catalytics.

If the car is running lean and a cylinder or 2 is misfiring, could trying to 'drive it out', actually make things worse/risk more damage?

Sorry for the long post, but thanks in advance for any help you can provide!

Could be a bad injector, that was the issue in my case. I had the P0306 code misfire cylinder 6.

Thanks Atrey! Did your CEL go on, or did you just connect it to a scanner and the error code was logged in there?

I know that's kind of a dumb question, but I'm not sure if our 4Runners can 'log a code' , but not throw a CEL.

If so, I will probably just hook up a scanner and check the log.

I had the code but it didn't throw a CEL light which was weird but that fixed my problem.

I don't know about the lack of a CEL, the computer stuff is a bit beyond me. I do know how to diagnose an engine the old fashioned way though!

Sounds like you might have some spark plug wires crossed... Did the symptoms appear immediately after changing your plugs and such? Often times, an engine will idle, maybe even move the car a little, but it won't rev and definitely doesn't have any torque. It'll also cause backfiring due to unburned fuel in the exhaust and be perceived as missing when it gets to a certain RPM or load.

X2 I can almost bet it is this cause my Tacoma had a bad injector and had the same symptoms as the OP. Give it some time it will probably throw a CE light

Thanks for the ideas guys! I don't think it's the wires, as they are NGK and worked fine immediately after swapping them out and worked fine for a couple hundred miles.

Am thinking it's likely an injector, due to running the gas tank down so low.

I will try to limp it over to an Auto Zone by my house and see if it's logging a code, even though there's no CEL.

Is there any risk of damage to the engine/fuel/exhaust system (ie Cat, O2 sensor...), in driving it short distances in this conditon? It's obviously not the safest thing to do, but I can take back raods, go slow and use my flashers.

Or...is there any other simple way I can check the injectors? I don't have a OBDII code reader and don't want to buy one. I heard you can sometimes use a stethescope, to 'listen' for the pulse/ticking sound of the injectors?

I'll probably do the fuel filter when I'm at it too...

Does everyone forget about the TPS? The TPS is what is responsible for the fuel air ratio. If you have it wide open, lots of skinny pedal, it tells the computer to increase the fuel mixture, or to decrease the fuel mixture. If the TPS is bad, it could cause the injectors to dump fuel into the cylinders, though the throttle is only open a little bit, causing it to big down because there is not enough air to properly ignite the amount of fuel because there is too much.

OP, if you stay high in the RPM range, does the truck run alright? I mean in the 3-6k range.

My 5lug had these same symptoms, yet when I would start in low, keep the RPMs high, it would rub fine because if was getting the right air fuel mixture. It also started throwing a 02 code, because the mixture wasn't right, as well as a misfire code.

If you know someone that had the same year Runner you have, see if you can swap the TPS. My bet is that's your problem.

Sorry for the spelling errors. Damn iPhone and it's autocorrect......

I didn't suggest the wires were bad, I suggest you mixed them up. I don't know the firing order on these engines off the top of my head, but if you have #4 on #6 and vice versa, it'll do exactly what you've described it doing.

Thanks, this info is great and gives me ideas of what else to look at.

I did not think of the TPS, but yes, it seems to run 'somewhat better', when I am revving it up. I haven't looked up a how-to on it, but it sounds cheaper and easier than throwing plugs, wires, injectors to it.

Wire numbering is not mixed up, as it ran fine for a couple weeks/couple hundred miles after doing the NGK plug/wires.

Although...someone who works at the Advance Auto, (said they have a '97 4Runner...) mentioned that sometimes if the plugs on our 3.4 motors aren't torqued correctly, they can be finicky. Any truth there?

I put my new NGK's in hand tight, plus a 1/2 turn, like I have with all my other vehicles, but maybe 1 or 2 spark plugs have loosened up?

He also suggested that maybe the boots on the end of the coil plug (ie where the coil plug connects to the spark plug...) can go bad over time and are replaceable.

I think I am going to try and limp it up to Advance and have them see if it has any codes logged and go from there.

I will let everyone know what the final verdict is, in case it helps someone else down the road who has a similar issue...

Thanks again for all the help and ideas!

Problem solved! It randomlly decides to clear itself up,when I fire her up and start heading over to Advance Auto, for the code reading.

Once I got there, they checked it, no codes found. I bought a bottle of Chevron Techron fuel system treatment, filled 'er up with some Shell V-Power 93 octane and drove about 50 miles, to get everything circulating again. Ran fine after that- normal acceleration, no bogging, no weak throttle response.

Only thing I can chalk it up to is either the issue is super-intermitent and it ends up coming back and is a bigger problem, or...it was infact just some crud that got sucked through the fuel system, when I ran the tank to low.

Note to self- don't run the gas tank that low and also, add a fuel filter PM to my list of projects!

Thanks for everyone's help and ideas, it definitely gives me knowledge of what to go after first, if this or a similar mis-fire problem occurs in the future!

if it comes back go get your injectors cleaned....funny these seem to be popping up everywhere now....this is how min acted when i had to get it replaced, took me a few weeks to actually get the code pulled as it was very random and intermittent.....still could be something else though, it just sounds exactly like mine did though , if it comes back in a few days let us know.

Glad you have it sorted.

Just a comment that the O2 sensors (which will throw a CEL) and a rattling or not functioning catalytic converter will not usually affect the running of the engine. I have a bad O2 sensor, rattling cat and an exhaust leak at the upstream O2 sensor and it runs as flawlessly as ever.

4 year old thread. Bet they figured it out.