RPM's jumping

[Lund79]

I have a 2001 Dodge Dakota Quad Cab, 4.7L with 72,100 miles. I've noticed recently (past month or so)that while driving on a straight section (using cruise or no cruise)that the engine will jump 2-300 RPM and then lower back down over a period od a couple sconds. It will do this randomly.

At first I thought it was only with the cruise on but have taken that off and still notice it acting this way. It doesn't seem like it is kicking into another gear (just increasing RPM). When I press on the accelerator I can get it to kick into the next gear and that jump in RPM is around 5-700 jump.

Do I need to be concerned? It is due for an oil change and will be taking it in for that soon. I have had this truck since new so know when things feel off. Thanks for the help.

[BoxMN]

No mechanic here, but I had a slightly similar issue happening with my trailblazaer, with 114k on it. It also rough (just slightly) rough at idle now and then.

I knew I was overdue as still on original plugs. Guys here told me to check that first. That was it. Running like a champ again, nice and smooth, and better mileage.

Maybe check plugs, and wires if you have them. Mine has coil packs, which actually made it pretty easy to change plugs in my model. Good luck.

[1968]

Running funny otherwise? Can your hear the engine speed up when the tach jumps?

If you haven't done plugs yet, it's past due for the SECOND replacement set already. Every 30k for this engine.

[Jeremy airjer W]

What speed are you traveling at? Sounds like it may be kicking out of overdrive?

[Macgyver55]

What speed are you traveling at? Sounds like it may be kicking out of overdrive?

Or maybe just unlocking the converter?

[dan z]

Ladies car was doing this over the weekend and the code said idle position control sensor.

[Lund79]

To answer a few questions that wwere raised.

1. I can't remember if plugs have been changed. I am not mechanical so I trust what my mechanic says that I should do. Will ask about this at the oil change.

2. Highway speeds is when I notice it (55- 65). Yes I can hear a change and feel the slight rev. At these speeds, it usually runs around 1,900 RPM. When it revs up it goes to around 2,200 RPM. Awhile back I had noticed a similar issue with when travelling from 60 MPH and then coasting to a stop light. When I reached around 45 MPH the engine would get a spike in RPM and then my MIL light would come on. Ended up checking that code and it was a O2 sensor (I believe)which was replaced.

3. Since it has started doing this, I have noticed the when starting my RPM's are higher (1,500 RPM) than what it usually runs (6-700 RPM). The engine will fluctuate in between these RPM's if I was to let it idle and then eventually they come down. Once it is started and I notice this fluctuation I usually wait a few seconds and then will press on the accelerator just a bit and the RPM's will settle down to the 500 RPM range and stay there.

I hope this info. helps a little more. I really appreciate all the help and suggestions so I can ask my mechanic if it could be this or that.

[Jeremy airjer W]

Ladies car was doing this over the weekend and the code said idle position control sensor.

?

Throttle position sensor or idle air control?

[Jeremy airjer W]

Dan your going to need a scan tool to take a look at a couple pieces of information. I'd be curious to see what the throttle position sensor is doing and what the computer is try to do with the IAC when the idle is high.

I think your feeling the vehicle kick out of overdrive. A flaky TPS can cause this. I like to check these with a lab scope. Most often the scan tool or a voltmeter are not fast enough to catch the dropout.

[Lund79]

Would bad/watered gas cause the issues I stated above? I ran the gas down until the low fuel light came on. Since filling up the tank, I have not noticed the RPM's jumping at highway speeds. I still have an oil change scheduled and am going to ask about the plugs too.