Throttle Position Diagnostics

Hello everyone. I have a a low mileage 2014 Prerunner 4L TRD Sport. I’ve noticed mediocre gas mileage (~15-16mpg) and a bit of wavering in throttle response mostly at low speeds and sometimes at highway speeds. I’ve cleaned the throttle body and MAF sensor and although the truck drives better, the hesitation has persisted. I have a OBDLink MX+ device hooked up and I do monitor the airflow. Today I added a monitor for the throttle body position. See photos below. Despite spirited driving, I couldn’t get the “absolute throttle body position” to get over 45%. It idles around 12% when stopped and generally ranges between 15 and 25% on the highway. The red arrow marker in the first photo shows the max when I drove as I normally do (max 30) and got to 45% when I pushed it hard (second photo). It is also interesting that the default range is 0-50 and not 0-100%. Do I have a problem and if so, what I can do to diagnose further? Thanks.

 

I wouldn't put too much stock into those values on a drive by wire system, it would almost certainly set codes if there was an issue with the throttle system as it is monitored very closely for any discrepancies. You could check and make sure your Accelerator Pedal Position Sensors are reading properly but that too will typically set a code.
You have to remember on a drive by wire system when you press the accelerator pedal your requesting the throttle to move but the ECM decides where to move it based on other factors besides accelerator pedal position.

Low MPG complaints can be very difficult to diagnose because there are a ton of variables involved and it could be fairly normal for your particular truck configuration and driving habits.

A couple things you can check pretty easily are:

Long and short term fuel trims under various driving conditions (should be +/-10% total (long term+short term) trim).

MAF sensor accuracy at idle and WOT, at hot idle MAF in Grams/Second (g/S) should be near equal to engine displacement in Liters (so 4 g/S for a 4.0L engine).

MAF accuracy/engine breathability on the top end can be checked by doing what's know as a VE (Volumetric Effeciency) test which is a wide open throttle pull through 1st gear while recording intake air temp, peak RPM, and peak MAF then entering the results into one of the calculators below.

https://otctools.com/ve
https://atgtraining.com/atg-volumetric-efficiency-calculator/

 

@Dm93, thanks for the detailed response. Working through your feedback. Added a monitor for fuel trims - OBDLink appears to only support total fuel trims and in my 20 min drive today that number stayed pretty much at 0. Also added the accelerator pedal position monitor and see the 2x relationship between position D and position E holds (don’t understand how to interpret the values though). Will work on the Volumetric Efficiency over the next couple of days.

 

That looks like the fusion app to me.
Mine had short and long term trims if I remember correctly.

 

Yes, mine does

 

Mine is the OBDLink app that goes with their MX+ device. I just looked and, you guys are right, was able to find them. Which of the 4 possible banks should I be monitoring? Thanks.

 

Banks 1(passenger) & 2(driver) side

 

Hi y’all, wanted to report back on this. Got the fuel trim PIDs on the app monitor and drove approx 50 miles over a couple of days. For the majority of time, the sums on both banks stayed in the -10% to +10% range. Figured that was within spec and working ok.


Rest of the story as follows. As I was doing these diagnostics, I also put in the anytime-fog-light mod. For that, I unhooked the battery (prob for like 20-30 mins). It must have reset the ECU as the truck is driving much smoother since. I’ve read about the battery trick in other posts and it didn’t even cross my mind to try it but it seems to have had some positive effect.