How to drop rpms. Im at 1,200 and need to be about 850. How do I achieve this???

Since only the ECM controls idle rpm, I think that you are going to have to provide some information regarding what your truck is and what repairs and symptoms that triggered high idle rpm. Details matter.

• John

Edited July 5Jul 5 by Tractorman

I have a 2000 some parts come 1999 dodge ram 2500 5.9 L 24 valve 4×4. I'd say a week ago I came out to go to the store and when I fired it up the rpms were high. Usually rpms are 850 but that night it jumped up to 1,200 rpms and has not dropped sens.

About a month earlier I started getting a dead pedal. I've changed the APPS , ECT and the BOOST. I've programmed APPS the correct way I've ran some electrical tests but im not real savvy at electrical stuff. I have p1693 and p0122 and a check engine light is on. My wait to start light is on constantly for 40 seconds before turning off.

When dead pedal happens going down the road I just have to let off throttle give it a little bit of time then give it a little throttle. If I put it to the floor it dead pedals again. Once I get to about 2,000 rpms it will dead pedal or if im going up hill.

I also have a spark coming off the harmonic balancer then jumps to the frount of the oil pan. Not sure what that's all about. I've cleaned all my grounds battery terminals my battery cables are good. I think that's about it if I think of anything else I'll post it.

P0122 - Accelerator Pedal Position Sensor Signal Voltage Too Low

Are you familiar with the W-T ground reference modification? If so, have you done the modification? This modification addresses a potentially poor ground splice for the ECM and many other components. It addresses other wiring issues, as well. The wiring diagram below shows how many components use this splice.

Here is the link to the Ground Reference Modification. I recommend to read thoroughly before beginning any work.

https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation/engine/electrical/ground-reference-vp44ecmpcmpdc-plus-tc-lockunlock-r567/?&tab=comments#comment-177452

• John

Edited July 6Jul 6 by Tractorman

Yes ive forgot to put this in as things ive done already . Sorry about that Thanks

Most likely a bad APPS sensor. The is a idle validation switch inside the APPS sensor. So if you have mess with or adjusted the sensor its possible you are stuck in throttle mode and idle will not happen. I suggest getting a Timbo's APPS and replace your APPS sensor, this should fix your idle issue.

No ELECTRONICS the Timbo's APPS is fully mechanical.

Now stock APPS. As you can see it requires electronics to make the idle validation work and misadjustment can and will affect idle speed.

So i just happened to unplug my ECT and started my pickup. My RPMS had dropped to 850. Now I plug the ECT back in and RPMS shoot back up to 1300 RPMS. Now what would be the cause of that ??? Cause its a brand new ECT straight out of a cummins box.

On 7/5/2025 at 2:35 PM, D-train69 said:

How to drop rpms. Im at 1,200 and need to be about 850. How do I achieve this???

4 minutes ago, D-train69 said:

So i just happened to unplug my ECT and started my pickup. My RPMS had dropped to 850. Now I plug the ECT back in and RPMS shoot back up to 1300 RPMS. Now what would be the cause of that ??? Cause its a brand new ECT straight out of a cummins box.

It almost sounds like the "high idle" is being activated. If you drive the truck with the coolant sensor disconnected, does the idle rpm stay where it should?

• John

On 7/5/2025 at 7:36 PM, D-train69 said:

I also have a spark coming off the harmonic balancer then jumps to the frount of the oil pan. Not sure what that's all about.

Some time ago, I did some research regarding this. It seems to be a bit of an anomaly that occurs on some vehicles when static electricity generated from the rubber part of the harmonic balancer jumps to the oil pan as a spark. The good news is that there is no cause for concern.

• John

Technically, the coolant sensor will control idle, but only in an OVERHEAT condition, it will drop existing RPM by about 400 RPMs. This is not the solution, but a normal reaction. I found this way back in the day by using a rheostat to vary coolant temperature. Just to let you know, this is a normal reaction to the sensor unplugged because it's a high volt code (+5V) and the ECM reacts accordingly.

Still, you have an APPS issue, most likely on the APPS sensor is not providing a proper idle validation signal. This will force the ECM to drop the APPS sensor signal and run the Cummins idle software, which is a perfect 800 RPM's.

Now the only other way to raise idle is bad injectors. If your injectors have over 100k miles you need to replace the injectors being as pop pressure falls and idle speed rises. I've seen trucks idling at ZERO percent engine load and idle speed of 900 RPM, being the ECM cannot cut fuel any deeper, and idle cannot be obtained.

Edited July 9Jul 9 by Mopar1973Man