DIY Network

Winter Maintenance: Servicing a Sticking Throttle From "Weekend Mechanic" episode WKM-308

The "dirty finger" test: a sooty residue around the interior of the throttle body, just behind the throttle plate, may explain why our accelerator is beginning to stick.

In this segment of DIY's Weekend Mechanic, host Bruce Bonebrake Bonebrake continues with winter maintenance on a GMC truck, including servicing and cleaning a sticking throttle-body.

Materials:

In addition to standard auto-mechanic's tools (wrenches, ratchets, extenders, screwdrivers, nut-drivers, torque wrench, etc.) and the snow-plow and hitch kits, the only specialty tools that will be needed for the projects in this episode are a fish wire, engine-degreaser spray, steering lube-kit and a level. An air-compressor and set of pneumatic tools is optional, but may be very helpful for this project.

DIY Difficulty Rating for the Projects: In summary, the projects shown in this episode are relatively basic and straightforward. We gave them a difficulty rating of 2 on a 5-point intermediate-level scale. It took us about 8 hours to finish the projects shown. Depending on the nature of the problems you might uncover, your work time could vary.

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Figure A

Servicing a Throttle Body

The throttle on our truck tends to "catch" or stick when the accelerator is depressed. This condition is likely due to a throttle body that has become dirty, a problem that is not uncommon. Here is a summary of the basic steps we followed to diagnose and solve this problem.

• Find the throttle cable that goes from the gas pedal to the throttle body. To do this, first remove the one bolt holding down the site cover on the engine (figure A).
  
• With the site cover removed, loosen the clamp that holds the air intake to the throttle body (figure B).

• The air-intake duct and resonator is stiff, so both clamps on both ends must be loosened before the entire assembly can be removed in one piece. After the clamp holding the air intake to the air filter box is removed, next remove the air intake assembly, with the resonator attached (figure C).

• Tip: As you remove the connecting parts from the throttle body, note which hoses are vacuum, coolant or air-duct. Use a white marker and write the letter "V," "C," or "A" to identify the connections.

  Figure B

  Figure C

  
  
• With the air-intake assembly removed, the throttle body can now be accessed for service or repair (figure D).

• Disconnect the throttle cable (figure E).

  Figure D

  Figure E

  
  
• Since the engine coolant runs through the throttle body, open the coolant reservoir so you can drain the coolant from the throttle body and the engine.

• Remove the electrical connections from the throttle body.

• Carefully pull off the vacuum lines and the coolant lines (figure F).

• Remove the three nuts holding the throttle body to the intake manifold. Once those three are removed, the throttle body can be slipped off the engine for cleaning (figure G).

  Figure F

  Figure G

  
  

  Figure H

• To clean the throttle body, use cleaner spray but avoid spraying the electrical connections (figure H).

• It's best to use carburetor cleaner and a soft shop rag to wipe the part clean. You can also use a soft toothbrush to loosen debris.

• Tip: Typically, you should clean the throttle body about every 30,000 miles.
  
• Once it is cleaned thoroughly, the throttle-body can be reinstalled. Adding a new gasket (figure I) is the first step in reinstallation.

• Position the throttle body and lightly push it into place to properly seat the new gasket (figure J). Tighten the throttle body back down on the manifold bolts.

  Figure I

  Figure J

  
  
• Reseat and clamp the coolant hoses, reattach the accelerator cable (figure K) and snap the electrical connections back in place (figure L).

  Figure K

  Figure L

  
  
• Ease the air duct assembly back into place and re-clamp it to the air cleaner and throttle body.

• Finally, add the coolant you drained back into the system. (If the coolant is more than a year or so old, replace it with new coolant solution.)

• Start the vehicle and run the engine to make sure the throttle is no longer sticking.

Important: Included in this segment are the steps in this automotive procedure as shown in the episode. These steps are general guidelines that are applicable to most vehicles. With any particular vehicle, there may be procedures, specifications, settings, tolerances, components, etc. that are specific to that vehicle. There are also variations according to the type and brand of repair-kit you select. Always consult your vehicle's service manual when undertaking significant automotive repairs, and read and follow the manufacturer's directions and precautions that come with your kit or replacement parts.

Safety Alert: As a standard safety precaution, always disconnect the vehicle's negative battery cable before you begin work on any electrical or mechanical components.

Safety Alert: Always dispose of automotive fluids (antifreeze, motor oil, transmission fluid, etc.) and other toxic substances responsibly. Most auto center offer recycling of automotive fluids.

RESOURCES :

The Complete Idiot's Guide to Trouble-Free Car Care
Author: Dan Ramsey
ISBN: 0028635833
Alpha Books

Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896