Erratic idling and stalling issues are so irritating; you’re on the right track, and a dirty throttle body could be the root cause. Cleaning shouldn’t take more than thirty minutes; before long, she’ll be on full song.
WD40 won’t be an effective throttle body cleaner; hard deposits stuck to the throttle body and throttle plate will require a throttle body solvent. Throttle body cleaner is formulated to help break down carbon and other fuel-related deposits on a throttle body.
I’ve been a mechanic for more than twenty years, and I’ve cleaned more throttle bodies than I count. In this post, you’ll learn how to clean your throttle body, and I’ll share a few tips along the way.
How Throttle Body Works
Once all throttle assemblies were a full mechanical affair. Rods, cables, and levers work in harmony. Pressing the gas pedal caused a direct physical movement of all this hardware. With the computer age came the fly-by-wire. The throttle pedal no longer has a cable attached; instead sends a proportional voltage to the onboard computer, the PCM (Power-train Control Module).
The PCM makes a few calculations and sends a proportional voltage to the throttle body’s stepper motor, which opens the throttle plate, sending you down the road.
The throttle body, made from cast alloy, looks like a pretty substantial mechanical component. But it is really an electronic component. The throttle body houses the all-important throttle plate but also a stepper motor and sensors.
The stepper does all the heavy lifting; it’s a precision kit. It’s tasked with opening the throttle plate just the right amount, too much, and the engine runs lean, too little, and she’s running rich.
The throttle body also contains sensors that report the throttle plate’s precise position; the PCM will use this information to make fine adjustments and to flag a fault. Accuracy is mission-critical.
Symptoms Of Dirty Throttle Body
The symptoms I’ll bet you are already very familiar with; some of these may ring a bell:
- Erratic idling – Engine doing its own thing
- Stalling – When you come to a stop
- Hard starting – Long crank
- Surging – Revving up all by itself
- MIL (Malfunction Indicator Light) set to on
- Hanging idle – When revved, the Rpm’s come down slowly and hang higher than normal
- Hard on gas – Eats gas
- Loss of power – Just no go in her anymore
Yep, you’re on the money; it seems like your throttle body needs to be cleaned.
Removing Throttle Body
Some throttle bodies are so difficult to access you’ll be tempted to remove them; I’ll caution against this action as PCM (Power-train Control Unit aka ECM or ECU) learned throttle positions may be lost.
The accelerator pedal and throttle body are in constant communication with the ECU, and the ECU knows what exactly each is doing and what position they are in. The ECU needs this constant feed of information so it can respond quickly to drivers’ commands.
The PCM adapts the position of the throttle body over time to allow for wear and tear on the throttle body.
Issues may arise when the throttle body’s wiring connector is disconnected. The PCM loses the adapted throttle body’s position and simply tries to reset the throttle body to new factory settings; this may cause your engine to idle erratically.
There is a throttle body relearn procedure. However, some vehicles may need a trip to the main dealer.
Cleaning Throttle Body
First, you’ll need a quality throttle body cleaner with a nice long straw. This stuff is specially formulated to break down heavy-duty carbon deposits; a cheap cleaner will make your life difficult, so a top brand is a way to go here.
This is a job for the outdoors, cos this stuff is hard on the lungs. You’ll need some tools, obviously:
- Fresh paint brush
Begin by removing the keys from the car; attempting this with the ignition on could damage the throttle and your fingers.
Remove the intake trunking and possibly the air-filter housing. Assess your plan of attack. Can you view the throttle plate? If not, angle your mirror and light so you can. Layout some plastic or some shop rags to catch the runoff; you don’t want this stuff running onto other components.
Spray the face of the throttle plate with a gloved hand, and press and hold open the throttle plate while you spray inside. Allow it to do its work for about ten minutes before repeating the procedure.
Problem areas include, around the throttle plate itself, a buildup of crap that prevents the plate from moving freely. The inner walls of the housing gather combustion-related buildup too. This also interferes with the natural flow of air through the body.
Use your shop rags to clean up the runoff; repeat this process as many times as necessary. Be sure the throttle plate area is completely free from carbon.
Intake & Fuel System Service
Your car’s intake system does require some maintenance. An intake service is recommended every 45,000 miles. The service includes a solvent solution that cleans the throttle body and the intake plenum.
The procedure takes about one hour and does require special shop equipment. The engine’s fuel system is disabled and instead fueled by the combustible solvent. It’s sprayed directly into the throttle body and cleans as it goes.
A dose of injector cleaner and lubricant is added to the gas tank. The MAF (Mass Air Flow) sensor is cleaned and new air filter finishes the job. Some vehicles will require a throttle body re-calibration, aka a re-learn procedure.
Throttle Position Re-learn Procedure
Throttle position relearn is different for all makes; typically, it’s done using a diagnostic scan tool that connects with the car’s onboard computer; the technician then commands PCM throttle relearn mode.
A manual solution is also an option, here’s a GM relearn procedure, just to give you a flavor.
- Idle the engine until it reaches operating temperature
- Turn engine off for at least one minute
- Idle the engine again for at least five minutes
- Drive the vehicle at a range of speeds using various acceleration/deceleration cycles (on and off throttle)
It is possible for fault codes and a check engine light to come on, if so just clear them and repeat the drive cycle again.
Most cars will eventually enter re-learn mode themselves, but others may need a date with the main dealer’s scan tool.
Can I clean the throttle body with Carburetor cleaner? Throttle body cleaner is a heavy-duty cleaner specially developed to break down hard carbon deposits. A carburetor cleaner could be used to clean the throttle body, but it won’t be as effective.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.