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goodwrench9124, ASE Certified Technician
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I have a 2000 Suburban, my tow/haul does not work, and the ...

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I have a 2000 Suburban, my tow/haul does not work, and the engine sometimes revs up, are these related problems, if so what should I look for?
hello, are you saying the tow/haul mode switch on shifter doesnt work, and when does it just seem to revs up????
Customer: replied 10 years ago.
sometimes after it is warmed up,it revs up to 1200 rpms, yes, the switch on the shifter doesnt work
ok normally the switch that is in the shifter on column, there are two wires that run out of the shifter inside the column usually will break they are very small wires. the column covers will have to be removed for inspection. your other concern about reving up, i thinking maybe trans is slipping under load???
Customer: replied 10 years ago.
when i am sitting in park it revs up
ok it has a idle concern, normally when the idle goes high it is caused by a vac leak. have you had a check engine light coming on???
Customer: replied 10 years ago.
no check engine light

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

Tow/Haul Switch/Indicator Always On or Inoperative (4.8L and 5.3L)

Object Number: 607409  Size: LF

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.

Document ID#(NNN) NNN-NNNN
2000 Chevrolet Chevy Suburban - 4WD


Subject:Increased Accelerator Pedal Effort, Idle Instability (Clean Throttle Body and Adjust Blade) #02-06-04-054B - (03/17/2003)


Models:1999-2002 Chevrolet Silverado
2000-2002 Chevrolet Suburban, Tahoe
2002 Chevrolet Avalanche
1999-2002 GMC Sierra
2000-2002 GMC Yukon, Yukon XL
with 4.8L or 5.3L V8 Engine (VINs V, T, Z -- RPOs LR4, LM7, L59)


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.

  1. Verify that the cause for this condition is not a damaged or binding throttle cable.
  2. Remove the air intake duct. Refer to Air Cleaner Duct Replacement.
  3. Inspect the vehicle for installation of a fixed orifice PCV valve, refer to Corporate Bulletin Number 01-06-01-029B for PCV valve identification. Vehicles undergoing this throttle body procedure MUST use a Fixed Orifice PCV Valve, P/N 12572717.
  4. Clean throttle body bore and throttle valve plate of carbon using a shop rag and an appropriate cleaner. Refer to Engine Controls Repair Procedures - Throttle Body Cleaning Procedure.
  5. Select the correct plug for the size of the air bypass hole in the throttle body being serviced. Use a 1/8-inch (.125") drill bit to determine which plug to use.
    Vehicles built before introduction of the Fixed Orifice PCV Valve will have a 3.75 mm (.150") air bypass hole in the throttle plate. The 1/8-inch drill bit is smaller than the air bypass hole in these throttle bodies and can be inserted into the bypass hole. To plug the air bypass hole in these vehicles requires the yellow plug, P/N 12580749.
    Vehicles built after introduction of the Fixed Orifice PCV Valve will have a 2.6 mm (.104") air bypass hole in the throttle plate. The 1/8-inch drill bit is larger than the air bypass hole in these throttle bodies and cannot be inserted into the bypass hole. To plug the air bypass hole in these vehicles requires the red plug, P/N 12581011.

    Object Number: 927140  Size: MF

  6. Insert the appropriate plug (1) into the air bypass hole in the throttle plate. Insert the "tail" end of the plug through the throttle plate air bypass hole.
    Object Number: 927142  Size: MF

  7. Open the throttle plate to allow access to the tail end of the plug. Pull the tail section to securely position the plug into the air bypass hole and trim excess material (1) from plug.
  8. Turn ignition key to the on position, with engine off.
  9. Use the Tech 2 Scan tool to read initial TPS voltage.

    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.

  10. Using the Tech 2 Scan tool and a T15 driver to rotate the Minimum Air Rate screw, increase TPS voltage by .08 Volts (Refer to TPS Voltage Chart below).
  11. Turn ignition key to the off position. Verify that the accelerator pedal moves freely - Depress the accelerator pedal to the floor and release.
  12. Install the air intake duct. Refer to Air Cleaner Duct Replacement.
  13. Start engine.
  14. Using the Tech 2 scan tool, monitor TPS voltage and verify the TPS voltage is no greater than 0.69V.
  15. Road Test Vehicle.

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.

TPS Voltage Chart

Initial TPS Voltage

TPS Voltage After .08 Volt Increase

0.45 V

0.53 V

0.47 V

0.55 V

0.49 V

0.57 V


0.59 V

0.53 V

0.61 V

0.55 V

0.63 V

0.57 V

0.65 V

0.59 V

0.67 V

0.61 V

0.69 V

If initial TPS voltage is greater than .61 V Replace Throttle Body Assembly

Parts Information

Part Number




Plug, Throttle Plate - Yellow



Plug, Throttle Plate - Red


Parts are currently available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation


Labor Time


Throttle Body - Clean and Adjust

0.6 hr



99 through 05 GEN III truck engines may experience any of the following:

  1. A cold rough idle that diminishes as the engine warms up.
  2. Possible DTCS P0171, P0174, or P0300.
  3. Random misfires at idle.



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.

  1. If leaking intake gasket seals are found, replace the intake gaskets. During the repair be sure to use the current GMSPO part number for replacement intake gaskets. The current GMSPO part number for intake gaskets will have a teal green intake gasket seal. The old version of the intake gaskets were orange in color. Use only the teal green colored gaskets for a repair.
  2. The intake plenum should also be checked for excessive warpage that may cause an uneven clamping pressure of the seal. If the plenum is found to be warped it will need to be replaced. Service Information states, "An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87 in) area should be replaced". Intake warpage is measured at the gasket sealing surfaces, and should be measured within a 200 mm (7.87 in) area. This measurement is across only two of the intake runner port openings. Measurements taken across the entire distance of all four intake runner ports will lead to unnecessary manifold replacements.

I hope this info was helpfull and anything you dont understand please ask me to explain

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