Idle effected by MPH / in gear

[Supreme Pizza]

2003 Suburban 4x4. 

 

Does anyone know if there are any vacuum lines that go to the tranny on this rig? 

 

At a dead stop, in park it idles at 600. Put it in gear and it stays at 600. 

 

Start moving forward and the idle will slowly climb up to 1100. Shift to N, and it bumps up to 1200, and then slowly drops down a little to about 900. Roll to a stop, and it drops back to 600. 

 

Going 70 MPH on the freeway. Shift to N, and it idles at 1600. 

 

The faster you go, the higher the idle is. 

 

Idle always returns to 600 at a dead stop. Any time you are moving, the idle is too high. 

 

 

 

 

 

[Supreme Pizza]

Found a brand new throttle body on Amazon for $125.50. I emailed the seller and talked them down to $75.55, with 2 day free shipping. Installed it, and the problem went away. Woo-hoo. The repair cost less than a "one hour" diagnostic at any local repair shop. 

 

 

 

 

 

 

Edited May 25, 2018 by starman8tdc

[Mike GMC]

Glad you got it fixed.  I would never have even seen that issue. I've never put it in neutral on the highway.