High idle above 3 MPH?

ROBTA

MEMBER
2003 DODGE RAM
5.7L
V8
4WD
MANUAL
300,000 MILES

When driving above 3 mph and the RPMs are at least 1,300 if you put it in neutral the RPMs will increase to at least 1,800 sometimes as high as 2,200. When they are below 1,300 to begin with, or when you go below 3 MPH, the RPMs return to a smooth 750 idle. If it receives no speed input by disconnecting all 3-wheel sensors, or by disconnecting the ABS control module, it operates completely normal.

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
43,048 POSTS

This sounds like you have a vacuum leak, use this guide when the engine is cold to help find it:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If no leaks are found, let's service the throttle body which the IAC motor is internal, check out this guide and look at the images below to show you how on your truck:

https://www.2carpros.com/articles/throttle-actuator-service

Also, we should run the codes and check out the high idle guide to help see what's going on.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

and

https://www.2carpros.com/articles/engine-idles-too-high

Check out the images (below). Please let us know what you find. We are interested to see what it is.

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Friday, October 7th, 2022 AT 2:56 PM

ROBTA

MEMBER
2 POSTS

No engine codes. It is not a vacuum leak, as I stated it runs fine if the speed sensors or anti-lock control module is unplugged. Nothing to do with the throttle body, APPS, or ECU, all have been replaced with no change in problem. Definitely speed related as it only begins above 3 MPH and stops doing it below 3 MPH. Cruise control works fine.

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Friday, October 7th, 2022 AT 4:20 PM

KEN L

MASTER CERTIFIED MECHANIC
43,048 POSTS

That's a good one, can we unplug the wheel speed sensors one at a time to see if the problem changes? How does the wiring harness look? have there been any modifications? Also, you say there are no engine codes, but have you run the ABS codes?

https://www.2carpros.com/articles/anti-lock-system-testing-and-repair-abs

Please let us know what you find. We are interested to see what it is.

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Saturday, October 8th, 2022 AT 10:00 AM