Problems with Throttle by Wire

[joezek]

Have this issue where I step on the gas lightly and nothing happens, then at about 1/4 throttle it lunges and takes off. Looking at it on the scan tool, the pedal sensor shows a perfectly smooth transition from 0-100%. The sensor called "R Throttle" whatever that is, shows 8% at idle, will move a little bit to 12%, and then during light pedal movement it will do nothing and then jump to 25 or 40%, or some other random percent in between.

Now here's the weird part- if I set the cruise control on the highway it shows the R-throttle steady around 12%. When I come to a hill then the R-throttle shows a perfectly smooth increase to about 25% while climbing the incline. But on straight level highway if I try to lightly step on the pedal, the R-throttle jumps all over the place from 20-45%. Meanwhile the actual pedal position sensor is showing a smooth reading and not jumping around.

I'm trying to figure out how the pedal is wired to everything. Since my scanner is showing a smooth transition, that should eliminate the pedal sensor and all the pedal wiring up to the computer since the computer is also forwarding that info to the live scan tool. I think the computer then sends the throttle request to the throttle body ETC motor. For some reason the ETC motor works perfectly fine with the cruise control but not from the pedal.

I'm lost as to what the problem is. Maybe the computer is screwed up. Anyone else have this problem?

 

[LokiWolf]

One useful thing would be the year?

I would still point at the Pedal Sensor. It is the most common failure in the system. Also the fact that cruise is smooth.

Swap it, and see if the issue goes away.

 

[joezek]

It's a 2008 EL XLT. The pedal has multiple wires so maybe the ones showing the output to the scanner are not the same as the output going to the computer/ETC? I'll look for the pedal sensor and replace it, see what happens.

I tried to do a throttle calibration but not sure if that did anything at all. It seems slightly smoother but still have a definite dead spot every time I go just above idle. In fact sometimes now it shows the pedal moving to around 15%, but engine still idling in gear, and then the R throttle and 3rd throttle sensor show a jump to WOT, and then quickly back to 20%......very weird.

 

[joezek]

None of the local parts stores have it in stock, but I found the part number on Rockauto which would have taken a week to get here. I found the same one made by Dorman on Amazon, will be here tomorrow supposedly. Was like $55, part # 699-132. I'll update if it fixes the problem. That would be nice, been getting worse since I bought the truck and never figured it out yet. I know it's killing my mileage too. Without cruise control on, my throttle is constantly jumping up and down but the truck just feels like an annoying surge. With Cruise set I seem to get about 15-16 mpg over a few mile average. Without the cruise it's around 12 mpg.