Dodge Diesel Cruise Issues

Torque converter lockup and release. Tire slip.

Suspect "TPS" —Throttle Position Sensor

It is the ground wire connected to your throttle sensor that feeds into your ECM for your transmission control, cut in half and tie directly to ground, eliminating the electrical noise carried through out, it worked for me and you will find it on the SUN Coast Diesel web page as well, they sell a kit $60 or you can do it yourself from Radio Shack or Wal Mart for that matter for around $5, up to you.

The CAB (Controller Antilock Brake) uses the wheel speed sensor on the rear axle for vehicle speed and the PCM gets it over the bus. if the signal from the WSS is erratic your cruise will surge. you probably will not feel it when using the pedal but the PCM see's it and will act up when cruise is on. check the sensor with a scope to see the wave. in one case i had, the rear axle was replaced. then i found out the carrier was dropped and dented the tone ring. this increased the air gap to the sensor and gave me an erratic signal causing the cruise control to surge. Another cause could be electrical interference from the harness. mainly the lift pump circuits. try cutting the WSS circuits out of the harness and running your own wires to the CAB.

Do you have a check engine light? I would have it scanned as a first option. Too many things can make an erratic idle while driving. I suggest an Autozone if one in near you, their Check Engine Light scans are free.

Things that could make the idle erratic:

- Vacuume leak

- Idle Air Control Valve (IACV)

- Throttle position sensor (TPS)

- Torque Convertor Clutch Solenoid (TCC)

- A very Lean or Rich fuel trim condition

- etc......

This being a Deisel there is no engine vacuum or IAC. the TPS or PPS (Pedal Position Sensor, there is no throttle plate so no TPS) could cause idle issues. Injector pump timing being out could also cause idle issues but very rare.

Yes, there is vacuum. The vacuum pump is located in front of the power steering pump. All of my Dodge diesels have surged a little with no load. Add a trailer and it smooths out.

As diesels do not produce vacuum, his has to have a pump to produce vacuum.

Ole, let us know what you find out as well are all hitting close to the same area

the dodge diesel has the same problem when off of cruise/ it surges and gains about 100 rpm up. and then back to normal. this might do this for a second or two and then back to normal . my not do it again for a time. thanks ole

Inspect both lift pump and injector pump. Low fuel delivery can cause injector pump failure.

On the newer computer controlled 24 valve engines, there isn't a direct connection between the "gas" pedal and the "throttle" as it were.
It is a "fly by wire" system, the APPS senses the position of the "go pedal" relays this to the computer and the computer tells the injector pump to add more fuel.
The computer also used the pedal position to regulate shifting in the auto tranny.

If it isn't working right, you'll have sluggish acceleration,
"hunting" shifting in the transmission, low power, etc.

On the 12 valves the TPS mostly controls the 3rd & 4th gear up and down shifts along with rpm.