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Throttle bodies get dirty and have to be cleaned obviously from time to time. As always, looking at the butterfly plate is never enough, the front is always clean looking. The horror show is on the back. My previous vehicle, GMC Envoy, was prone to getting a bouncing idle speed and eventually stalling if the throttle body got really, realllllllly dirty. That was because a dirty throttle plate gets sticky, making the computer controlled, electronic throttle body unresponsive to the PCM's commands, leading to over-compensation (the bouncing idle).

Just recently clean the girlfriend's throttle body. It's from a 2009 Ford Focus.
Here's the back side....
Auto part Engine


That's why you must take it off!

That was at 60,000 Km. Not very high mileage. Thank the EGR system for this. the port on the right side of the throttle plate is the EGR. Because it is behind the throttle plate injecting exhaust into the intake, it gets stuck in an eddy of air current. From there it cools and sticks to the back of the throttle plate. Not sure our cars have EGR... I'll find out soon enough when I get to it.

Cleaned with cheap aerosol throttle body cleaner (don't use brake cleaner, not good for seals!). Wear latex gloves!
Auto part Automotive engine part


Just like my old GMC that was prone to running rough from a dirty throttle body, the Focus smoothed out a fair bit and was more responsive.

I haven't cleaned the throttle body on my Cruze yet because I'm only at 34,000 Km right now, but at 3.5 years old I'll do it next time I change my oil anyway. I've seen a few post about rough and uneven idle speeds related to the poor PCV design, but I figured I should share my experience because of the similar symptoms to two different problems. Simply cleaning of the throttle body resulted in a much smoother running vehicle on both my SUV and the girlfriend's Focus, so it may be something to keep in mind with our cars too.
 

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The EGR really does make a mess out of the intake and TB.
 
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The 1.4T (and lots of other cars these days) do EGR with variable valve timing now that it is common on both intake and exhaust camshafts. Should make less of a mess and eliminates the need for actual EGR valves that are prone to clog with mileage.

There's often a crankcase ventilation (PCV) hose right in front of the throttle body, though. On the 1.4T, there is one on the intake side of the turbocharger that gets a little messy, and another right in front of the air filter element that should keep that crap out of the system.

So far, mine is fairly clean. Others have reported significant amounts of oil @ the throttle body.


That one's on the intake side of the turbocharger.

 

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The 2.0 Diesel is the only Cruze with an actual EGR system.
Which will lead to unwanted carbon build up in the intake side of the engine.
 

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The EGR really does make a mess out of the intake and TB.
your right about that. the diesels are worse. i never had that problem on mine...


whats funny i thought the gas engines would be a little bit cleaner...
 

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Can see problems with the Fords, least the ones I had, some idiot elected to return the PCV valve back into the air cleaner where all that garbage would build up in the TB, was a constant job of cleaning it. Where others were returning that garbage return line into the intake manifold.

This wasn't much of a problem with carburetor vehicles, but new problems with fuel injectors, that carbon would build up on the face of the injectors affecting the spray pattern. Only way I know to effectively clean them is to remove them. I see where the Cruze is returning this garbage line to the turbo, again going through the TB, may be convenient for production, but more problems for the consumer.

To lengthen the time between manual cleaning, should only use top tier gasoline, but top tier really had not been defined. Carbon build up on the rings increases the blowby with even more garbage to get in there. Kind of like a self destructive machine. So I dump in a can of Seafoam about every 5K miles or so, to help keep the engine clean.

Clean engine, less blowby, less problems and only use top tier gasoline. May save a couple of cents, but sure would have to pay a steep price later.

Carbon in gas is an age old problem, we tried to get rid of it in the 70's, very little heating value and makes a mess. Plus CO will kill you, but now have a hundred years, making an issue about CO2.

Can see where this servo driven vane can be more of a problems as opposed to linkage with a strong return spring. Moving parts that also need cleaning and lubrication. And any lubrication will dry up over time and heat.

One way to solve these kinds of problems is to trade your vehicle off every three years, and this is what they want us to do. Replacing a worn out brush is no longer a solution to keep all these electric motors running or a cheap bushing. Making this stuff throwaway now, so we have to replace the entire component.

Their idea of recycling is not replacing just an extremely inexpensive wearing part, but to cook the whole thing down and make a new one. And they call this progress.
 
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