Throttle position dropping when accelerating. ETCS-i issue ?

Long, but please read my post before trouble shooting my Tundra acceleration issue.

Throttle position dropping during acceleration but accelerator pedal position not changing.

2013 Tundra 4WD 5.7 3URFE. This is not a flex fuel truck.

I purchased this truck used in February of 2019. It was a one owner truck, sold at auction to a used car dealer that I purchased it from. No service records, clean car fax, 90,000 miles. Clean truck. Leather seats, vinyl floors, double cab, 8' bed. My dream Tundra minus the stupid nannies and lack of real LSDs and lockers.

My problem after purchase:

Hesitation on light acceleration within a few miles of buying it. Drives good at highway speed.

Jumping forward to 6/17/2019. The throttle position is dropping when my foot is still requesting acceleration.
I have replaced the throttle body and MAF sensor with new Toyota factory parts. Fuel pressure is not an issue via Toyota diagnostic service appointment.
Running Stock air filter with no vacuum leaks detected.
This has to be an ETCS-I issue with no faults recognized in ECM!

Note: I have also witnessed the absolute throttle position to drop down to 0% during normal deceleration and after a full second of applying the breaks see the throttle position jump back up to 2.4 % throttle position. The truck lunges forward, but is held back by the brakes, because my foot is already on the brakes.

I am monitoring live data with a BlueDriver and iPhone.

No CELs.

I have turned the nannies off, no difference, tow haul on/off no difference.

2 hour diagnosis at Toyota Dealer: ruled out fuel pump and fuel pressure issue by way of mechanical gage connected to fuel rail during test drive with Techstream.
Acceleration hesitation was very problematic during dealer test drive.
Fuel pressure was always in the 40 + or - range.
I was driving my truck, with Toyota master mechanic riding shotgun with laptop Techstream live.

Toyota Technician tried a new MAF sensor midway through diagnostic. No change with acceleration problem with new MAF.
Diagnostic ended with the "only thing left is try an ECM reset with battery disconnect"

ECM reset by battery disconnection solves this problem consistently for 30-40 miles of stop and go driving around town. Mileage longer at highway travel. ​

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I have replaced the MAF and complete throttle body with Toyota factory parts as a means to throw new parts at it vs. pay the dealer more labor.​

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I am monitoring accelerator pedal data and it is not dropping and changing like the throttle position data is showing.​

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What's next Tundras.com? HELP ME! ​

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My local dealer doesn't even know what to say. ​

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Or come buy this Lemon of a truck from me.! I'll make a sweet trade if you have a Sprinter van with I5 or I4 motor. $ +or minus on TRADE​

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I'm in $26,500. ​

Reasonable losses considered on a sale, but I'd much rather fix and keep truck. ​

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Time for me to contact the NHTSA? ​

Acceleration witnessed when I'm on the brake only!!!!!!!!!!!!!!!!!!!!!!​

 

Have you tried selecting manual gear mode and driving in only 6th gear?

Selecting 6th gear and leaving it there actually puts it in normal mode. There won't be any assisted engine/trans(?) breaking. Is less aggressive on down shifts, and few other things.

May be worth a test.

 

Since you've replaced the throttle body (new throttle position sensor and throttle control motor) with no change in symptoms, you have to assume the throttle position sensor is good, but the position sensor electrical output to the ECM is being corrupted. OR, alternately, the ECM interpretation/processing of the signal it's getting is bogus.

Reset of the ECM fixing the problem for a few miles indicates to me the problem is in the ECM, and not in any of the wiring. I would consider buying a junk yard ECM with matching part number and change it out before I would dump the truck. I did that once on a 22RE that wouldn't start, but in my case, the real problem was far worse...the timing chain had slipped few teeth. I didn't know those old Toyota ECMs were highly reliable. I finally ebayed that old ECM after it sat in a drawer for a decade or so, and got most of my money back.

 

I don’t notice any difference between 6th gear in S mode and D. Same engine braking from what I’ve noticed as well as same downshift tendencies.

 

Really? I'm basing it off of someone else's information but when I tried 6th in s mode for a while I remembered thinking it was noticeable.

I dunno now, placebo effect maybe?

 

Maybe, but I could be tripping myself LOL. I haven’t really noticed much of a difference between the two other than it locking out in whatever gear it’s placed in. I could be wrong.

 

We do have a good few years difference in our trucks. I'm just gonna go with we are obviously both right.

I'm good with that.

 

I’m good with that!

 

That's pretty weird. Sounds like your ECU or the programming is bad. I didn't read anywhere that the did a re-flash, so maybe that's what needs to happen. If everything is running right after the ECU is reset, it sounds like that's your problem.

 

Thanks for weighing in everyone.

I was ready to purchase a used ECM but my local dealer discouraged me stating the computers generally work or don't work.

The technician also had no other advice for me, so the discouragement was not a push in the right direction to keep moving forward.

ECM and or Accelerator pedal look like the next best steps for me to take.

 

Tried this tonight. Truck still has throttle position dropping out with foot on the accelerator.

 

Do these trucks have a throttle position sensor that could be going bad? In my past experience on other brands this has usually caused erratic idling though.

 

Wish I could help. Good luck. I’ll be interested to know what it was when you find it.

 

That was my first thought, but the throttle position sensor and the throttle control motor (either could be the cause of this problem) are integrated into the throttle body. If either of those is diagnosed as bad, the service manual says to replace the throttle body. He replaced the throttle body, so both of those are new.

The accelerator pedal assembly is the other likely culprit. Trouble-shooting the pedal assembly with a multi-meter might be possible.

He said the dealer, who has no idea how to fix this, says "computers either work or they don't", so it can't be the ECM. For $200, I think I would buy a used ECM, plug it in, and try it. If it's not the ECM, then I would ebay the used ECM and my get money back. He'll be back where he started and smarter, but will have saved the money to have the dealer re-flash his ECM.

Edit: Uh-oh, one issue with the used ECM idea. The used ECM will be expecting a different key to disarm the immobilizer. That can get the OP is a ****-load of trouble. Trash that used ECM idea @Lifeonwheels, unless you have Techstream to reprogram the used ECM to your existing key.

 

I think troubleshooting the pedal assembly would be my next step. I’ve been trying to learn how to use my multi meter. Need to figure out the ohms and check the resistance?

 

The throttle body has to sensors inside it. I replaced my throttle body with a new factory Toyota complete assembly so my TPS sensors are new and did not resolve my problem.

The accelerator pedal has two sensors in it as well. I am tempted to replace mine but the live data for the accelerator sensors is not dropping off like my throttle position is.

 

I have been looking into the immobilizer issue for used ECU swap.
Does anyone know if these second gen Tundra's have a DYI immobilizer relearn process through jumping the correct pins at the OBD2 port and waiting with key on for 30 minutes.

 

Seems like that be no deterrent for a thief to work around...unlikely in my opinion.

 

I would have to figure it out as well, but I'm thinking you would to need to look at voltage output from the pedal assembly...maybe signal to ECM? Resistance may also work, and you wouldn't need to turn ignition switch on.

 

I went ahead and ordered a pedal assembly. The new way to diagnose: throw new parts at it. Pedal should be here in a few days.

Google this if you want some interesting reading: Tin whisker analysis of Toyota's electronic throttle controls

Here is a link to the PDF: https://www.autosafety.org/sites/default/files/imce_staff_uploads/Tin_whisker.pdf

 

Nice find on the paper.

I think you're going to get lucky throwing a new accelerator pedal assembly at it. At least you got a clean throttle body out of this.

 

Installed new Toyota factory gas pedal assembly today. Completed ECU battery disconnect reset at the same time.

Bad acceleration issue still present. Issue re-surfaced after 5 miles of driving.

Live Data: Relative throttle position is dropping back down to 0% throttle position when I get the hard stumble. ( With foot on accelerator pedal)

Also experienced another unwanted change from 0% throttle jumping up to 2-3% throttle by itself when my foot is on the brake with no accelerator pedal depressed.

This sucks.

I have a $40 junk yard ECM on order. eBay seller wouldn't answer any questions so who knows if its any good. I figured for $40 its worth buying even if its just a core.

Anybody know if I can write the used ECM to my 2013 Tundra without techstream? It looks like the early Toyota electronic throttle control vehicles could DYI re-write the immobilizer via OBD2 port pinning and proper procedure.

This YouTube video references 2007 Toyota:

https://www.bing.com/videos/search?...71FCA99C724DDE1428C671FCA99C724DDE1&FORM=VIRE

 

How about doing a continuity test between the wires from the pedal assembly inside the cab to the throttlebody. Could it just be a bad connection?

 

So hard to test since the continuity is sufficient to send signal.

Interesting fact I have not posted yet: I cannot duplicate the throttle position dropping off if the transmission is in neutral or reverse.

 

Here is another ECU immobilizer reset video on 2012 Lexus:

https://www.youtube.com/watch?v=QocuEYNE6KM

 

Almost fixed!!!!!!!!!!!!!

My $40 eBay ECM never showed up.
I dropped $950 on a new factory Toyota ECM.
Didn't need it.

I looks like I have a intermittent short in the main engine wire harness.

The loom that exits the ECM and passes under the heater hoses and over the passenger side valve cover is the likely location of my short. THIS MIGHT BE VALUABLE INFORMATION FOR ALL 5.7 Liter Toyota's. If you have an intermittent hesitation or feelings of improper transmission shifts, check your harness in this location. Pull, tug, tap the harness with engine running. Move the harness around with the truck running in park and in drive if you have a helper to sit in the truck and hold the brakes.

I was amble to tap this location with the truck running in park and get the engine to stumble. I removed the factory zip ties, tape, and conduit to start looking for the weak wire or wires.
Can't find it now that the wires are loosened up and relaxed. I'm able to tug and pull on every wire individually with the engine running in park, no detection of engine stumble or hesitation. Just drove around 400 trouble free miles of city and highway miles. I have added some zip ties back to try and recreate the original harness shape and stresses, but that was 400 trouble free miles ago.

I'll find it and repair. Once I do I'll post more.

Almost certain it's not a connector or electronic part problem.
Likely a wire stretched and weakened internally: At the place the flexible engine harness exiting the ECM meets the plastic conduit clamp bolted to the rear of the engine.

 

My condolences on your trouble, sir, but I salute you. Your tireless patience and persistence in pursuit of such an outrageously irrational issue is an example to us all. In your place, I would probably just leave those zip ties in place forever.

 

Fixed:

Small yellow and red wire spliced.
Picuture attached.

Outer Insulation looked great. Wire may have been torn inside. Tried to slice open the 1.25” of wire I cut out but it was hard to tell. I’d have to say it’s likely the wire was completely broken inside the insulation.
Working by the ends touching most of the time.
Engine movement put a slight stress at the poor connection.

Anybody have a wire schematic and knows what this yellow and red wire is ?

 

Outstanding detective work! I had a little time this morning and took a stab at id of the wire.

I found a 2015 ECM wiring diagram, and there is a red/yellow wire from throttle position sensor ("VTA", connector D9, terminal 6) to the ECM ("VTA1", connector A24(A)/D74(B), terminal 78).

It all makes sense now. If you had the wiring schematic, you could have checked all the wires from throttle position sensor to ECM for continuity, but then you would still have to shake the harness to discover the discontinuity. Being lucky (and highly motivated) is better than being smart.

 

Thanks for the write up, going through a similar thing on a new 2021. Having issues with the dealer and warranty, this issue happened twice with in about 4000 miles when I purchased the truck. Dealer said they didn't find anything and said the flashed and update the ECU. Now I have a SC, injectors and a few other modes and saying it's the SC giving the P2111 code. UGH. I think it's the pedal which I'm replacing tomorrow. however it sucks that Toyota is unwilling to even investigate. ALSO the drivers seat rocks back and forth and the dealer claims it's a faulty seat braked, which has been on back order for 11 months.

Again thanks for the write-up and ideas as I troubleshoot a truck with 14,000 miles on it because the dealer refuses to investigate. stay away from Stapp/Interstate Toyota in Colorado.