Mystery intermittent hesitation/stumble from a stop?

So, I have searched for some answers to an issue I am having and I have found a little info, but nothing definitive so I am hoping someone may have an answer!

I have a 2014 Taco with a 4.0 with 123,000 miles on it. I am experiencing a slight but very noticeable hesitation just after stepping on the accelerator pedal from a stop. If I heavy foot the pedal there is no hesitation, the hesitation only happens when I accelerate at a "normal" rate. And to increase difficulty diagnosing the issue the hesitation does not happen every time, but it happens most of the time. I also tested to see if the hesitation happened if I accelerated (with hesitation) then immediately stop and accelerate again; there is no hesitation when I re-accelerate from a stop.

The hesitation started happening after I installed a new air filter, removed charcoal secondary filter, cleaned MAF sensor and cleaned the air box. The spark plugs have about 10K on them. I ran a scan with a Snap-On Apollo D8 and there are no codes present. The idle is smooth and normal RPM's and truck runs at 100% while moving (no hesitation at all while moving). I just have an annoying stumble just after stepping on the gas from a stop. To a passenger in the truck it feels like the driver is backing off of the accelerator momentarily. Finally, I had an HP Tune installed recently which ended up amplifying the hesitation. The hesitation existed before the Tune was flashed. I had my fingers crossed that the HP flash would fix the hesitation.

I have not check the VVT screens yet so I am aware that may be the issue. But, I stopped by my local dealer to purchase new screens and they told me they have never sold those screens, zero sales. So, I suspect the likelihood of the screens being plugged is not very high.

Thanks for reading and I appreciate any help offered!

 

I seem to recall a thread within the past couple of months where @Dm93, @gearcruncher, or another frequent "incredibly helpful individual" described the drive-by-wire nature of the accelerator and where a hesitation might stem from. IIRC there was the pickup sensor connected to the gas pedal, and something associated in the throttle body. I'll see if I can track it down.

 

Did you disconnect the battery after cleaning MAF/throttle body to “reset” the computer so it can re-learn? There was just another thread about that too.

Can you revert/roll back the tune without too much headaches to eliminate any possible issues there?

 

I disconnected the battery to do a reset after the cleaning and I also did a TPS specific reset just the other day. I could have the tune taken off with some effort but the hesitation was there before the tune was done. The tune amplified the hesitation a bit but the hesitation was definitely there before the tune. Thanks for the ideas...keep them coming!

 

If you find the thread that would be great! I searched for a bit for possible causes and came up short on anything more than what I have already done.

 

Lol. That member MAY be me.

OP, you have exactly what I had for YEARS on my truck. No codes, everything otherwise clean and no reason for it to occur. I even checked fuel pressure to make sure it wasn't happening. I checked everything down to even data logging the truck and seeing what sensor or solenoid was causing it. To no avail. I finally fixed it BUT, I have seen absolutely no mention of you cleaning the throttle body, so you need to do that first before you do anything else because I don't want you tossing money at it for no reason.

Do that and get back to me.

 

I failed to mention I did clean the TB when I cleaned the MAF, new air filter, etc. It is squeaky clean! Thanks and I am curious what is behind door #3!

 

This next one is EASY. Hit your traction control button for 3 seconds until Auto LSD and TRAC OFF turn on. Take your truck for a spin and try to replicate it. If it goes away, problem solved!

If not replace both VVTi solenoids, pull the battery terminals for a good minute to clear out it's running condition, wash your hands and call it a day.

 

The problem started after you replaced the air filter? Is a oiled K+N? Put the old filter back in and see if that helps

And/or hook up a scan tool and watch fuel trims while accelerating. Trims will tell you if the fuel system is working properly

 

I will try turning the traction control off today and check it out. If it turns out the hesitation is gone with the traction control disabled then I can only assume the issue is temporarily bypassed while the traction control is disabled. If that is the case do you know the root cause of the issue so it can be fixed so the hesitation is fixed while the traction control is activated?

Then onto VVTi solenoids!

 

It was VVT solenoids and screens that fixed this exact problem for me. Don't overlook them if all else fails.

 

I replaced a K&N filter with a Napa Gold. The reason I removed the K&N is when I removed the charcoal secondary filter there was quite a bit a dust on the inside of the air box just in front of the throttle body. And I have read that a K&N offers more air flow but may not be the best filter vs a high quality paper element. If there are any airflow issues between the 2 filters then an ECU reset should have reset the air/fuel ratio right?

I ended up replacing the MAF with a new Denso unit attempting to fix the hesitation just in case K&N oil messed up the existing MAF. The new MAF did not make a difference.

I will also watch fuel trims to see what happens.

Thanks for all of the input!

 

Okay, so in yet another thread, it was mentioned that care should be taken when cleaning the throttle body, in particular not forcing open the butterfly valve manually as it could cause an issue in the motor/gear mechanism. I read that AFTER I had cleaned mine and done exactly that, of course, but thankfully no issues arose. I think it's a rather low probability cause, but still I mention it as, like @b_r_o said, since the truck wasn't doing it before the servicing but it is doing it now, anything that was done come first on the list of possibilities.

The VVT solenoids/screens have come up in a number of threads but usually in the P0012 (and associated) code topics. I suppose a solenoid could have coincidentally gone bad but it seems less likely.

 

Pop the coils out and see if the tips are oil covered or dry. Oil covered would mean it’s time for valve cover and spark plug tube gaskets

 

I definitely manually opened the butterfly to clean the throttle body. I learn something new almost every day! That would suck if i damaged the TB but it is an easy fix if so. I suspect I should be able to run a scan on the TB when accelerating to see if there is a disruption that occurs.

 

I'm not sure what I just read there. If the issue is a TC issue then there is no fix for that other than killing the program. You can always rig a switch to kill ABS and TC all the time. Does that make it right? No it doesn't, but the TC/ ABS/ Stability control program on these trucks suck so, not much we can do there but be better drivers.

 

UPDATE!!! Hesitation is fixed. Since I did not have any codes to work with I started replacing parts that I touched when cleaning the MAF and TB. The first item I replaced was the MAF and that did not fix the issue. The second item I replaced was the throttle body thinking I may have messed it up by manually opening the butterfly. Turns out that did not fix the issue. Then based on information provided by 12TRDTacoma I moved onto the VVT system. I pulled the passenger side screen to see if it was plugged causing an oil flow restriction. The screen was 100% clog free. My next step was to replace both VVT solenoids which turned out to be the winner! The hesitation is 100% fixed.

With no codes present I suspected the "bad" solenoids would test to be good. Both solenoids tested at 6.9 ohms of resistance which is perfect. I then tested the mechanical operation of both solenoids by connecting the electrical leads to a 12 volt battery. Both plungers moved freely and the same distance. I did not see any visible clogging and it seems that both solenoids are 100% functional. I did not test the new solenoids to see what the distance the plunger moves on them but I suspect they would be the same as my "bad" solenoids.

So, if I had tested the original solenoids before purchasing and installing new solenoids they would have tested 100% functional. I would have reinstalled the original solenoids resulting in continued search for the cause of the hesitation. I am relieved I installed new solenoids before testing the original solenoids because I would still be chasing the issue and quite possibly could have been chasing the issue for years. I hope this helps someone in the future hoping to fix their hesitation!

 

Exlnt

 

This is a great thread. I'm having this issue on my 2014 TRD Sport. I will definitely be using this to diag. Awsome community!

 

So after some diagnostics with the scam tool and pro demand I have found the following;


Injection Volume (Cylinder 1) Spec 0.005-0.015 ml Idling I have a reading of 0.101ml.

Idle Spark advance readings of cyl 1 (10) cyl 2 (0) cyl 3 (2) cyl 4 (0) cyl 5 (0) cyl 6 (4).

Short them fuel trim rich on bank 1 and lean on bank 2.

And a MAF reading of 3.78gm idling and 10.5gm and 2000rpm specs are 3.2-4.7 idling and 13.1-18.9 at 2000 RPM

Running a compression test and injector cut out test resulted in no tangible results.


My guess is that I may have a leaking injector or and injector with an uncalibrated injection or worn ports along with a MAF that's going out. The thing is that I have no loss of power and no issues in Open Loop. My issue is a slight rough idle and a stumble on normal acceleration when in Closed loop. Slow acceleration you don't feel anything and hard acceleration its still there but the stumble is much shorter. Thoughts?