odonnell

I've searched around, but so far haven't been able to find someone with a similar issue.

When cold, the truck starts and drives great. After ~5 mins of driving, there seems to be a loss of power. Not unusable, but, maybe 20-30hp loss. The car still rolls forward with no gas pedal (it's an auto) but not with much power as it used to. When accelerating, it just seems sluggish compared to what I'm used to.

Warm starts are a little sketchy. If I restart the car within ~1 min of killing it, it fires up almost instantaneously. But after sitting for ~2-45 mins, there is some hesitation during cranking, like it's not getting enough fuel. But when it catches, it runs and idles perfectly fine (minus the lack of power thing).

165,xxx on it, auto, 4WD. I run good fluids and have new Denso dual-electrode plugs in it, new NGK wires, coils are in spec, new air filter, tires at correct PSI, trans fluid in check and at right level, etc. Basically all the normal stuff adds up. No check engine light, doesn't smell like it's running rich. No rotten egg smell from the cat. I was thinking, maybe a sensor that controls the fuel mixture with respect to coolant temp? Just spitballing based on my other EFI adventures.

Thanks for any insight guys.

TacomaJunkiey1968

Odonnell,
You definitely have me stumped, but I am not an expert by any stretch of the imagination. Here are some suggestions which might help your dilemma. First, I would clean out the entire Mass-Air Flow unit and replace the sensors and filters in this unit. Next, I would start looking at the fuel delivery system. Replace the fuel filter, which should be done every 30,000 miles. Lastly, I would look at emission stuff , which is probably not going to be the problem since your 4Runner is not throwing any computer codes. You also might want to try and get it to throw a code just to make sure your 4Runner's computer is working properly.
Good Luck.
Paul
1999 Tacoma V6 5-Speed

odonnell

Paul,
Thanks for the tips. I just got a new fuel filter which I'll install this weekend, and I'll grab some MAF cleaner, can't hurt. It stumps me as well... it wasn't a gradual thing, it happened almost suddenly. I can't pinpoint it exactly since the rig isn't my daily, but we'll see. I'll report back...

TacomaJunkiey1968

Yeah Odonnell,
Your dilemma is quite perplexing especially since it happened all of a sudden, which means some part or sensor is broken or something is clogged.
Good Luck once again Odonnel.
Paul

TacomaJunkiey1968

Hello Odonnell,
I am completely refraining myself from telling all of my Irish jokes. LOL.


I have thought about your problem a little more. This is just a theory, but it might be worth exploring. It sounds like it might be exhaust. Something in the catalytic converter or muffler might be expanding once the engine comes up to temperature, which is inhibiting exhaust flow. Therefore, reducing the engine's power. Catalytic converters have a lot of precious metals, which can do strange things especially as they age.


The fuel delivery suggestion I gave you yesterday is more than likely not going to be the culprit because the fuel's temperature directly reflects whatever is going on in the environment. Other than the fact, it doesn't freeze.


Good Luck.
Paul

ThorInc

Once it cools down give it a good whack then and see if you can unclog it.

odonnell

Thanks for the tips guys. I investigated the exhaust further - it free-revs fine in neutral and it doesn't bog down at higher rpm like you would expect with a clogged cat.

Also after driving it more, I determined it's affected when cold, as well, just not as obvious because generally I drive easier when it's still warming up.

So that turns this into... What are your best guesses for why power could be down? The normal maintenance has been done, so I suspect a sensor (coolant temp? O2?) but I'm not familiar with the EFI in these trucks yet. Still no CEL.

odonnell

Still working on the solution. It's just weird, because the shift points are all where they always have been - the motor doesn't rev higher to compensate for the lower power. And I know I'm not imagining things.

I've narrowed it down to fueling... probably a faulty sensor, or a vacuum leak that I haven't found yet. I don't want to throw parts at it, so anyone know which sensors are notorious for aging the quickest?

Also, does anyone have information on knock sensor failure/degradation? It could be heavy spark retard from erroneous knock readings.

TacomaJunkiey1968

Odonnell,


Unfortunately, from what you said, your 4Runner's on board computer is not throwing any CEL codes, which makes your truck's lack of power very hard to diagnose.


Unfortunately, I am out of ideas. I wish I could provide you some insight, but I have exhausted all of my ideas.


Paul

75w90mantraN

Here are my suggestions:

-x2 on the fuel filter replacement and MAF cleaning.
-possibly fuel injector-related??
-changed PCV valve yet? Real easy to do. Could contribute to your issues.
-the sensor before your cat, has that been changed yet? They can affect drivability without setting codes yet. Good for 60-100k miles usually depending on how its driven. Has everything to do with fuel adjustments.
-It's assumed that the CEL comes on and turns off as part of typical engine startup. If the CEL never comes on with cranking, I'd suspect a bulb needs to be replaced in the dashboard. And if that's what's going on, well...grab a code reader or have them pulled for you free at auto parts stores.
-A clogged cat would probably set off a code by now.
-Vac leaks, like dirty MAFs, would make your idling go all over the place as well. Rentable vac pump could easily rule out vac leak. Or you can google starter fluid trick (but flammable)
-Just another maintenance to check off, but is batt good to go? No electrical issues?
-For me, I'm picky where I gas mine from. I stay away from local ones that aren't top tier. To each their own.

My bet's on fuel filter, dirty MAF, I forget if it's air/fuel or oxygen sensor 1 for your emissions type, and PCV, and possibly fuel injector(s) as any one or combination of things affecting you from joining the 200,000 mile club.

Good luck! Give an update when you fix it! It's a great feeling.

odonnell

Thanks for the reply!

I replaced the fuel filter about a week ago...I've had the part since last october but had been lazy about it. Old one was a 2004 part, and coffee-looking fuel came out the tank side. Still feels down on power, but I noticed the idle was a little smoother which is good. Also have tie rod ends and sway bar bushings to throw on this weekend, weather allowing.

I picked up some MAF cleaner today and will report back on that, as well as test the PCV valve. I'll replace it (and grommet, right?) with one from the Toyota dealer regardless, just for feelings.

The O2 sensors were replaced a few years ago but I'm not ruling them out either... I'm just trying to avoid throwing parts at the issue... ~$50 each.

I think I may have found something though. While I was inspecting the new fuel filter for leaks at the fittings (car running), I noticed some condensation on the welds for the cat. Someone had installed a new (maybe aftermarket?) cat a few years ago, and the welds look like hellen keller had a go at them. Perhaps the post-cat O2 sensor is getting false readings... but wouldn't that trigger a CEL with a code for bad cat? Correct me if I'm wrong, but the post-cat sensor is there for checking the cat and not for fuel trim.

By the way, I get CEL during cranking so I know it's not burned out. I also scanned the OBDII with a handheld scanner my buddy owns... 0 codes.

75w90mantraN

That's a big help to get your hands on a scan tool. Hopefully that particular one you got can reassure you of the MAF, oxygen sensors, and cat converter working properly. Yes, you're right, the post cat sensor only measures cat performance. The pre-cat sensor monitors fuel trims.

The pcv valve should come with a grommet. I just used Autozone. Dealer of course is best.

Can't speak to condensation on the converter welds. Don't think that would mean anything to engine performance. A clogged cat however, is a different ballgame...but I would think you'd have a CEL by now.

Post updates as you go along. Good luck!

odonnell

This is weird, but the issue may be resolved. I changed the outer tie rods this past weekend because the old ones were shot. Maybe I'm crazy but it feels a lot quicker... The old ones were very loose and I'm thinking that allowed toe on both front wheels that added a lot to the force needed to accelerate. Anyone experienced similar? I'll continue replacing worn parts...