Rpms jumping while in drive. Fine when in park.

[BigBlue05]

So here lately while in drive if I come to a stop my rpms jump around 50-100 rpms. Its slight but you can definitely feel it. However while im in park I can idle all day and the rpms are fine. Also noticed today that while it does it the lights dim just a little and when the rpms come back up the lights brighten up. Could this be an alternator issue? If not what could it be.

 

[finally03gt]

Just shooting from the hip..... I'd have an alternator load test run, make sure the throttle body is clean, and I don't know if it's throttle body or if they have a separate idle air control but that would be my next guess

 

[Jason G Slabaugh]

Throttle position sensor, I assume no codes?

 

[Redtruck-VA]

The first thing I'd do is put a charger on it overnight and see if that changes anything. Check the power steering fluid level. The power steering on g3 have a pressure switch that jumps rpm 50-100 rpm when senses high pressure. You can check it by unplugging it with the engine running and rpm will change.

 

[BigBlue05]

Also I should clarify when in say jumping. They drop from around 700rpm to 600-650 then go back up.

 

[BigBlue05]

So had the battery tested and the alternator. Both tested fine. Had a CEL. P2305. This is what is stumping me. I had the code pop up before. And fixed it or so I thought. When the code first popped up the truck would stumble while driving about 40mph. Changed the plug and coil and that problem went away. But the code never did. Truck ran fine no problems at all. The about 2 or 3 weeks later the problem i have now is happening and the same code is there. What should I be looking at?

 

[Karlsweg]

Have you changed spark plugs lately and if so did you put something other than factory recommendation of coppers champions back in?

 

[BigBlue05]

Have you changed spark plugs lately and if so did you put something other than factory recommendation of coppers champions back in?

Recently no. I changed them about 40k miles ago and yes I put champion coppers in.

 

[Karlsweg]

Recently no. I changed them about 40k miles ago and yes I put champion coppers in.

I would pull the “easy ones” to get to and check them. In all reality it only takes one bad one to throw a misfire. I replace mine after 30,000. Just be sure you don’t drop them down the hole and close the gap! I used a piece of gas line to lower them in and start them. And be sure to put never seize on the threads. The 05s have spark plug wires? If so this also could be a problem. The old start it at night and see if you see spark jumping from the wires. Preferably pitch black and hood light pulled. Just trying the easy basics for you without laying out money for parts you don’t need.

 

[Karlsweg]

Any updates?

 

[BigBlue05]

Any updates?

Not yet. Been raining and like 30 degrees. Finally got some Sun today. Hoping to dig into it and see what I see.

 

[BigBlue05]

Update: finally got to lookimg today and noticed a broken wired heading to the coil. Found a piece if wire laying around and wired it together and it seems tonhave fixed it. Havent driven it yet as I'm also cleaning my air filter. Will update after ive driven it.

Also that is by no means permanent.

 

[Karlsweg]

Glad it appears to be easy fix.

 

[Redtruck-VA]

Well done..

 

[BigBlue05]

Well I am pleased to say that was definetly the problem. Took it on a drive and on the way back the cel went away and the problem is gone.
Scared me for a while. With almost 210k miles you start to worry that every problem is a major one.

 

[Karlsweg]

Nice!!!!

 

[BipolarXpress]

I've had odd RPM issues with my Ram 1500 Hemi as well. I seem to have fixed it. Spark plugs were good. I ended up replacing a o2 sensor that didn't really fix the issue. I would idle rough and die at red lights at random times. If I was driving in town roughly 30mph it would stutter. I ended up changing the EGR Valve and the problem went away.