My 2006 expedition surges very slightly while cruising under very low throttle. Usually most noticeable at 60-65 mph with no headwind.

Took it in and had my mechanic check it out. He confirmed the slight surge and said it felt like the torque converter was locking and unlocking. No codes or pending codes were found related to the power train.

Abs light is on for a bad rear wheel speed sensor. Code for right rear. Checking the sensor showed 3 ohms for right, 5 ohms left ( left is less than a year old on a new wheel bearing.)

Initial thought was the bad sensor is giving bad input confusing the pcm/tcm. But the condition remains with the sensor unplugged.

Driving down the road watching the tach, it does appear that the converter is not staying locked. Conditon goes away with more throttle. Motor runs smoothly otherwise with no indications of misfire. Plugs have 50k miles on them, as does the transmission fluid. Fluid is red and smells fine. Never gotten hotter than 210 by the gauge in the pressure port.

I'm a little stumped. Why would it lock/unlock at very low throttle, but lock tight with more throttle? Tps flaking out? Throttle body motor getting twitchy?

Any ideas?

Can I pull my popup to the hills this weekend?

 

I would check the tps first; it is an indication from your symptoms. Use an analog volt-ohm meter on the wiper and one and of the sensor, and turn it to watch for smooth change in either ohms (disconnected) or volts (connected, key on).

 

I just installed a new one. I was going to try and troubleshoot the old one, but one of the bolts broke off during removal. After that much grief the old one was destined for the trash no matter what.

Normally id do more checking before throwing a part at it hoping it sticks, but I'm short on time, so I took the $80 gamble. I'm hoping this helps. I'll know tomorrow morning.

 

Quick update.

The TPS seems to have fixed the issue. I've put over 1,000 miles on since the change and I haven't felt it surge and the rpms seem to be rock solid at any throttle angle.

Not the approach I'd normally take, but it worked out this time.