i have included the tow haul switch wiring for you to look at, i going to do a little research for your idle so can you give me a few mins to review
there is a tsb for a unstable idle and also states for oil consumption. what this tsb is stating that excessive carbon build up in throttle body which allows air to enter engine. also there is another area to look at on these trucks are the intakes, like to leak vac causing various running problems. you can take some carb cleaner and spray where the intake meets the heads and if the idles changes, you know the intake is leaking vac.
This bulletin is being revised to add condition information. Please discard Corporate Bulletin Number 02-06-04-054A (Section 06-Engine).
Some customers may comment on an idle instability and/or a higher than expected accelerator pedal effort from the idle position.
Condition may be caused by deposits in the throttle body bore and on the throttle plate.
Important: This procedure only applies to cable actuated throttle bodies on the models listed above. This procedure should not be performed on electronically controlled throttle bodies or on any vehicle or engine that is not listed above in the Models section.
Important: TPS voltage cannot exceed .69 V. If the vehicle has an initial TPS voltage greater than .61 V, replace the Throttle Body Assembly. This part is currently on parts restriction. Contact the General Motors Powertrain Quality Center at(NNN) NNN-NNNNfor assistance.
Important: If an increased accelerator pedal effort condition still exists after performing this bulletin, throttle body replacement may be required. Please contact the General Motors Powertrain Quality Center at(NNN) NNN-NNNNfor assistance, as the throttle body is currently on a parts restriction program.
Initial TPS Voltage
TPS Voltage After .08 Volt Increase
If initial TPS voltage is greater than .61 V Replace Throttle Body Assembly
Plug, Throttle Plate - Yellow
Plug, Throttle Plate - Red
Parts are currently available from GMSPO.
For vehicles repaired under warranty, use:
Throttle Body - Clean and Adjust
99 through 05 GEN III truck engines may experience any of the following:
The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. The technician may also notice lower than normal MAF readings if the intake seals are leaking.
I hope this info was helpfull and anything you dont understand please ask me to explain