Acceleration dead spot

Hi, Just signed up and have a question that has probably been asked a million times.
2008 Tacoma Pre Runner, 4L V6, Automatic, 90,000 miles, second owner.

Occasionally when pulling away from a stop the vehicle will move off normally then stop accelerating. The motor does not die, the motor does not race, no shudder, no abnormal noise. It just simply stops accelerating. After 1 or 2 seconds it resumes normal acceleration. This occurs very infrequently. Could be twice a day, or a month apart, or maybe 6 months apart. Just when I think it will never do it again it does it. I took it to a dealer who drove it and of course it did not act up. Dealer just poo pooed it and said maybe the intake needed cleaning. I said power was great, not sluggish at all, transmission shifted fine, no slipping. Fuel mileage is normal at about 20 mpg. Does everything perfect except the the occasional dead zone on acceleration. The dead period is possibly connected with the 1-2 shift but I can't conform that. It does not do it often enough to really diagnose it. It catches me by surprise. By the time I think I should look at the tach or feed more gas, it resumes acceleration on its own. The dead period is maybe 1 to 2 seconds but when puling into traffic it seems much longer. So far it has only done it under light to normal acceleration. I rarely jack rabbit start so I can't say if it would act up under that condition. I have not been able to find a time or place to way to make it act up. It just does it on its own when ever it feels like it. It has done it with the transmission in both D and 4. Seems to do it at random, not under any specific driving condition.
Transmission fluid was changed with a pan drop and filter change. Toyota World Standard fluid used. Followed the posted fluid change procedure except non 4 wheel drive trucks don't seen to have a fluid temp sensor. Idled 15 min and used the check plug to drain excess fluid. I suppose fluid level might not be perfect.

So what's going on and how do I fix it? Will Toyota do anything about it? Is this a known problem?

 

Torque converter locking/unlocking is my guess. Also the prerunner does indeed have a at temp light unless toyota changed something with the 08 model year.

 

I searched the owners manual and there was no identification of a trans temp light for a Pre Runner. I followed the jumper procedure and no temp light ever came on. If it has a trans temp light, I do not know how to access it.

This delay in acceleration occurs at quite a low speed. Would a torque converter lock occur at 10 mph on the 1-2 shift under light acceleration?

 

Read this:

https://www.tacomaworld.com/threads/power-loss-surging.518439/#post-16404737

 

Thanks for the suggestion but that does not seem to fit my symptoms. There is no general loss of power prior to or after the dead zone disappears. As soon as the dead zone goes away I can step on the gas and it goes like hell. It is hard to describe what happens. Pull up to a stop, idle normal for a short time for traffic to clear, transmission has auto shifted to 1st. Step on the gas and the truck pulls away normally. Then acceleration stops completely just as if I had lifted off the gas, this occurs at a low speed right about the 1-2 shift. Maybe connected to the 1-2 shift. Maintain accelerator position. After 1 or 2 seconds acceleration resumes. At this point I can floor it ad all the power is there. During that brief dead zone period there is no power no acceleration. After the dead zone all is perfectly normal. This happens at random and only very occasionally. A few times I have been on the ball enough to advance the throttle during the dead period but nothing happens. I'm pretty sure the engine control computer is shutting the throttle plate for some reason. Is it normal for the computer to close the throttle briefly during and up-shift? Damn I wish it was not throttle by wire.

 

Sorry man, I didn't understand that it occurred at the shift rather than off the line. Otherwise it sounds just like what I described in the thread.

 

Almost sounds similar to a faulty throttle position sensor. A simple ohms test of the sensor will tell you if it’s faulty. I don’t know the values for testing. Could also be many other sensors

 

No reason not to try that. Cheap, needs doing as part of PM anyway. Nothing lost if it doesn't work. Be sure to get Throttle Body cleaner, not carb cleaner.

That's where I was going. Sometimes they just get 'flat spots'.

 

Today I did the throttle body cleaning. To do any good the throttle body needs to be removed. It was kind of dirty beyond the throttle plate but doubtful that will affect my acceleration dead spot. No way to know since it only does it infrequently. The TB has an O ring seal to the manifold so removal/reinstall is easy. The TB motor and TPS are sealed units. No service or repair. If those are a problem the TB will need replacement.

My feeling is the computer is shutting the throttle due to some program or sensor malfunction. Hope it does not kill me before I figure it out. Still wish it was not throttle by wire. When cars start taking over the driving it is time to say enough is enough.

Anyone with more ideas?

 

I have the exact same issue with my 2007 Taco (V6). Will accelerate normal until about 2,500 rpms and then pause, not a power loss, just pause. If I take my foot off the gas and then push it back down the truck accelerates as normal.

Here's the weird thing that caused the issue to start; I hydroplaned the truck across two lanes of traffic, 40 feet down a hill, and then did a couple of 360's to luckily come to a stop unscathed. I hit nothing, I did have to throw it into 4WD to get out of the mud and back on the road, but I switched back to 2WD Hi before I got off the grass. Ever since then I have had the issue.

After reading this thread I am thinking it might be the throttle body got clogged when I was jostling around. Regardless, I wanted you to know you weren't the only one with this issue as well as tell you the particulars of my situation. You never know what some of you wizards will piece together with seemingly unrelated information.

Good luck to you and I will report back if I make any progress with cleaning the throttle body, etc.

 

a few years ago mine did this and has not happened since

try to take off and it starts ok and acts dead like I took my foot off the throttle

only thing I can think of is maybe some fuel separated and the alcohol was being burned off

 

This happens so seldom it is hard to diagnose. Throttle body cleaning did not cure it. PCV valve corrected the idle speed but did not cure the dead spot. Possible causes of dead spot are - ignition, fuel, transmission or the computer control of the throttle plate. Transmission does not slip, motor RPMs do not increase, motor does not shutter or die or backfire. Does not seem like fuel. If it were fuel why would all 6 cylinders loose power at the same time. Does not seem like ignition. No hickups. So I'm stuck with the impression the computer has a mind of its own and occasionally shuts the throttle plate then almost immediately brings it back to the throttle pedal setting. Very odd. Still wish it had a throttle cable and not the throttle by wire system with a motorized throttle body. Does not repeat often enough to be a bad TPS. I do not need to take my foot of the throttle. Acceleration returns on its own in a second or so.

 

Check the brake switch down on the brake pedal. If it gets activated at the same time as the throttle the throttle is deactivated by the ECU. This was a software change brought on the the "Toyota unintended acceleration" Fiasco years ago.

 

WOW- what a great tip. I am a left foot brake-er. I'll check that out. I'd love it if it was just me screwing up and not the Tacoma. But you know I can keep the brake on and add throttle to move the truck in parking situations. So maybe it is speed related where the brake kills the throttle. Thanks for the tip.

 

test it by going a certain speed and start pusshing the brake and keeping throttle pushing at the same time. Throttle will shut off til you let off the brake.. Does it mimic the same symptom?

 

If the truck got the computer update for unintended acceleration it will lose power when riding the brake and accelerating. It will go to a point and then nothing. Let go of the brake and it goes again.

 

Nope that's not it. After many repeated attempts throttle, acceleration, and brake it might have acted up once. But clearly the brake does not deactivate the throttle. Full throttle, apply brake, continues to accelerate UN-affected. If I accelerate from a stop with the brake partly applied then release the brake it seemed like once the throttle took a dip but can't be sure. Could not repeat any abnormal behavior.

Now I wonder if there was a re-programing to deactivate the throttle with brake application that did not take and now it's goofy. It does seem like there might be a connection with the brake causing the random momentary throttle deactivation. Best guess so far.

Would a Toyota dealer be able to tell me what the ECU program is and test to see if it is programed correctly?

 

Hmm, mine shuts off when you hit brake and throttle

 

Checkout https://www.toyota.com/owners

 

I would check for codes. Next I would either scope or take the truck to a shop that have the capability and means of scoping the TPS. If there is a dead spot which is occurring as often as you say it will rear it's head during the testing process.

If it is the TPS, sorry my brother, but the entire Throttle body assembly will require replacement.