Air, Gum and goo

Modern engines produce more power, provide greatly improved fuel economy, and last longer than any engines in automotive history. If that sounds too good to be true, to some extent it is.

Maintaining high levels of performance and economy requires that drivers approach their vehicles in a proactive manner. Simply put, most preventive maintenance services must now be done before there are obvious symptoms. Often, waiting until symptoms are evident escalates costs far beyond what they would have been if the component or system had been routinely, proactively serviced.

A good example is Induction System Cleaning. Induction systems are comprised of a series of parts that meter, control, and channel air into the engine’s cylinders.

The induction system starts at the throttle-body. Throttle-bodies control the quantity of air entering the engine through an internal throttle-plate. Control comes from the accelerator pedal, which is connected directly to the throttle-plate. Depressing the accelerator opens the throttle-plate allowing more air to enter the engine. Simultaneous with pedal movement the vehicle’s computer senses the increased incoming air, adds an appropriate amount of fuel and the engine speeds up. Releasing the pedal decreases airflow and the engine slows down.

After the throttle-body is the upper air-plenum. This is essentially a series of molded tubes or pipes that direct air into the engine. The throttle-body is bolted to the incoming end of the upper air-plenum.

Last of the air induction parts is the lower air-plenum or intake manifold. The lower plenum is mounted between the upper air-plenum and the engine and completes the pathway for air to flow into the engine.

The biggest problem with these components is, they get dirty. Not from the air passing through them but from oily crankcase fumes. The Positive Crankcase Ventilation (PCV) system dumps contaminated crankcase fumes into the plenum directly behind the throttle-body. Over time, oil leaches out of the fumes and forms air-restricting sludge in the plenum.

Another routine problem is a varnish-like residue from gasoline vapors. Although no gasoline actually passes through the plenum, each time an intake valve opens to allow a fresh charge of air into a cylinder, turbulence pushes a fine mist of gasoline back into the plenum. Because the plenum metal is hot the mist is slowly cooked into a gooey varnish on the plenum’s inner walls and in the throttle body. The deposits may cause decreased fuel economy, lowered performance, rough idle, stalling, and hard starting.

Some engines are designed with a second set of throttle plates in the plenum to provide more power during hard acceleration. These “butterflies” are opened and closed by a vacuum or electric motor. Without routine Induction System Cleaning the “butterflies” become seized, which often leads-to a several-hundred dollar parts replacement.

Unlike fuel injector and carbon depletion services, which address parts following the induction system, Induction System Cleaning removes the dirt, sludge and varnish inside the plenum. Induction System Cleaning should be performed every twenty four to thirty thousand miles.

Also, to prevent damage to seals and gaskets a relatively mild cleaner is used for Induction System Cleaning. Therefore, Induction System Cleaning will not replace the much more aggressive carbon cleaning service.

© Copyright 05/15/03 Pat Goss all rights reserved


Dave Herrera said:

March 3, 2015 at 11:58 am

Any advice on how to find and choose a vendor for induction cleaning?

Marcy said:

March 3, 2015 at 12:24 pm

Hi Dave,

We use and recommend BG Products. To find other shops in your area that also use BG Products try and then do your research from there.


Jack Adkins said:

March 3, 2015 at 12:39 pm

I have a 2008 Jeep Grand Cherokee Limited with the MB 3.0L turbo diesel engine. Does this engine also require Induction System Cleaning? Does an auto repair shop need to perform this or is it a gasoline tank additive? Thank you in advance for your advice. You are a godsend fro us auto owners. We have appreciated your advice throughout the years.

Marcy said:

May 19, 2015 at 12:54 pm


Not in the sense that you put anything in the tank or inject it through the intake but as they age they sometimes need to disassembled (air intake system not the engine) and manually cleaned. Additives like BG 44K or their dedicated diesel additive keeps injectors and fuel system parts clean but because all diesels are direct injection (fuel is injected directly into the cylinder not onto the intake valve)it does nothing for the intake system. Even manual cleaning isn’t needed that often on a Benz engine due to design. When things do need service other than listed in the owner’s manual you will start having performance problems like hard starting sluggish acceleration or smoke from the exhaust (white or black).

Pat Goss

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