I have a 2003 Dakota SLT, 4.7 V8. Manual transmission, 140,000 miles. The engine has been having issues with low idle after shifting out of gear; for instance, shifting into neutral when approaching a stop light, or shifting out of reverse after backing up. The RPMs drop below 500, it shudders a little, then pops back to right above 500. Occasionally, this actually stalls the engine. Once it "bounces" below 500 and comes back up, the truck idles pretty nice at full stop. The issue just seems to be with shifting out of gear, and apparently rolling in neutral. Thoughts on what it could be?

The critical symptoms:

• Generally speaking, the issue is worse when the engine is cold. Stalling tends to happen more before it heats up.
• The issue is slightly worse when on an incline, as are common in Seattle.
• Strangely, when I let the truck roll in neutral (eg. downhill) the tach bounces back and forth from about 300 - 600 rpms!
• The check engine light is NOT on. I haven't had anyone plug in to check codes. No fluid leaks or anything.
• Otherwise, the truck runs GREAT when it's in gear!

The good news:
Luckily, I'm already deep in the middle of the truck's mid-life tune up, so hopefully the list of possible culprits is short. Relevant things I've already done:

• New spark plugs
• Cleaned the throttle body (plus a seafoam spray top-end)
• New IAC valve
• New TPS
• New MAP sensor
• New PCV
• New battery & alternator
• Brand new oil in there
• Brand new air filter

My next thought is a vacuum leak somewhere in the lines; that's gotta be it, right?

I've also seen a few posts referencing the possibility of it being transmission-related, but am not sure if that's more relevant to the autos. For reference, I had the fluid replaced when I picked it up at about 118k, but the transmission was on the ground around 135k when I put in a new clutch.

I am happy to pull the throttle body apart again and re-check all the new sensors, etc, but not sure it will make a difference. Was pretty thorough the first time through. Here is a quick video showing the strange RPM dance when going down a hill in neutral:
https://drive.google.com/file/d/1Clm...ew?usp=sharing

 

Welcome to the forum.

It is not transmission related.

For the sensors, did you go OEM? Not all sensors are the same and some aftermarket ones just don't work very well.

Did you take the throttle body off to clean it?

Just for kicks, turn the a/c on and see what happens to the RPM.

 

Thanks man.

There was some snake-oil talk I saw somewhere about a transmission seal that caused a leak or some madness but I couldn't possibly see how it was related.

Anyways, I managed to get my hands on a reader today. No engine codes at all (just one ABS 'incident' code).

Definitely was rougher today than yesterday, especially when the engine was cold. I managed to stall it a number of times and came close to stalling in the middle of stop and go traffic once or twice. It has zero issues cranking over to start when it's cold or after it stalls... the strangest part to me is that it's idling pretty calm at about 600 RPM, AFTER I've come to a full stop and it stabilizes. The issue only happens when I go from moving to slowing down / higher RPMs down to low. It's also really weird that the tachometer dances up and down when I'm rolling even out of gear, but doesn't when I'm at full-stop.

During installation, I pulled the intake manifold off and used throttle body cleaner on / around the throttle plate, and inside the housing for the IAC valve. Was pretty thorough about it but did not remove the whole throttle body, I guess. I'd imagine the seafoam spray through the top end would clean most of the deeper gunk out?

As far as sensors go, I did not go OEM. I grabbed a significantly more expensive TPS at O'Reilly today and put it in (BWD). No major change after installing it and resetting the computer; although it didn't stall on the way home, I think it's most likely because the engine was warm.

I DID notice that it stalls significantly more often when the A/C / blower is OFF. Running the A/C seems to do a better job stabilizing it?

I guess I can replace the MAP sensor again, too.... The brand was Airtex, I think.

 

Take the throttle body off and clean it. Seafoam won't do it.

You also didn't need a reader. Your truck can display codes itself.

 

Holy crap - nice tip on the codes! Youtube provides! I had no clue. That's a neat trick.

Took the dak out on the highway last night and put it to a good test. It's running great in every way when it's in gear or shifting, so I think the newer TPS is working pretty well. Just that weird idle / tach dance when rolling, but that seemed to get better after 30 min of driving.

Did notice that the drop is a lot more dramatic when falling from higher RPMs to neutral (eg. third gear on highway) than when I throttle down closer to 500 RPM and then let it drop. May be on drugs, but I also thought cranking the power steering while popping to neutral (like reversing out of a parking spot) made the drop worse.

Hokay. I will pull the whole throttle body off and give it a deep clean and see if she runs better. Recommend replacing any gaskets while I'm in there?

 

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There is also a power steering pressure switch that is supposed to bump up the rpm's when you put a heavy demand on the system.

Sounds like the IAC is slow to respond.

 

Nice. I figured that might be the case but wasn't sure if I was on drugs. I'll pull the IAC out and clean it / the port as well when I clean the throttle body. Would rather avoid replacing all three new parts with even more new parts.. Can you see my replies? They are hidden for some reason on my screen