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2.0 Petrol Engine (1Az-Fse) - Rumours Of Carbon Build-Up

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Browsing a forum on the (New Zealand) Automobile Association website whilst researching options for a new car for a family member, I noticed repeated advice to avoid the D-4 petrol engines because of carbon build-up causing problems such as rough idling. The recommendation to owners of the engine was to use 98 Octane fuel to minimise the problem. (Example here)

As I had recently bought a 2 litre petrol Avensis (2007) with D-4 VVT-i engine (1AZ-FSE) this naturally set some alarm bells ringing - i.e. what should I do about it?

Having spent a while trolling the web elsewhere for information about this I am inclined to think that the problems occurred with an earlier D-4 petrol engine, not this one.

Is there any hard evidence that the 1AZ-FSE engine is subject to such problems? I believe it is also used in the RAV4.

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I have not experienced or heard of any such problems until this day.

The mitsubishi direct injection petrol engines had some issues, but never heard of

any problem on the toyota ones.

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I used to own a 2Ltr Avensis with the same engine.

I put 190,000 miles on it and never came across this problem.

As said above, I have not heard of this either.

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Comments so far are reassuring, thanks, it'll be interesting to see if anyone else knows more.

The only reference to such a problem that I was able to find on the web, other than the original NZ AA forum, was an item about the first generation (2001-2005) Premio on the Kenya Toyota Club homepage

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No I have to say I've not heard anything about the 2.0 vvti and carbon build up.Usually when a car has a known issue theres page after page on the internet about it.

It seems a bit odd though as most modern petrol engines build up very little carbon compared to engines 15 ~ 20 year ago.

Are they talking about carbon fouling the plugs or build up on the combustion chambers,valves and piston crowds ??

I don't really see what switching to 98 oct fuel will do.Putting higher octane fuel in will only help if either you alter the the timing to make use of the extra knock resistance or it's knocking already.

If carbon has built up enough to make it miss then changing fuel isnt much of a fix.

The only thing I can think is perhaps the engine is in a different state of tune in NZ,perhaps for emissions reasons or the quality of the fuel over there as I've never heard anything like i over here.


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The assertion has been that the buildup is in the intake tracks - here's another example (all these assertions are coming from the same one or two expert voices in the NZ AA forum).

Presumably the engine computer will be continually adjusting timing to match the fuel characteristics??

I don't think our petrol is inferior to that elsewhere in the world, though until recent years I believe our diesel used to be somewhat inferior to European diesel and caused grief with some high-end Euro diesel cars here.

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  • 7 months later...

Another New Zealander here with the same car and the same engine who also became similarly concerned when I read the comments on the NZ AA website.

In my experience (and my own opinion), running BP Ultimate 98 RON for 3 consecutive tank fulls in the car made the engine less smooth overall -- rougher acceleration, rougher idle, rumbling when cruising along at 50km/h at low RPM (Auto transmission), 10% worse mileage (all 3 tank fulls), in fact, I felt that the engine actually ran better on that initial fill of BP Regular 91 RON (when I first got the car) strangely enough!

Switched to using Caltex Techron Premium and Z ZX Premium (Both 95 RON) and the engine performed much more smoothly overall and this is what I've been filling the tank up with ever since I got the car almost a year ago. Haven't noticed any problems (yet), engine is still running smoothly. As far as I've been able to decipher, 95 is the recommended RON for this engine.

The fact is though, more and more of these gasoline direct injection motors are appearing on the NZ market such as SkyActiv, Ecoboost, SIDI. I've known 3 other people who drive the NZ New 2003-2008 Avensis wagons with the same 1AZ-FSE D4 engine and they have put about 200,000km on the car and said they were unaware of such problems.

Not sure if anyone has any experience with this, but there are comments around the place that spraying some Upper engine cleaner every now and again through the air intake, might be able to reduce (but not eliminate of course) the carbon build up enough so that it doesn't cause a problem?

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Thanks for the input. Interesting comments about the fuel. I had been thinking that BP 98 was probably the most cost-effective option but recent running on Caltex 95 is showing quite good economy.

I did get a bit worried when idle suddenly became quite rumbly but have concluded that it only happens from time to time when the aircon compressor is running - as if the computer isn't asking for quite enough power from engine and it is labouring a little as a result. Haven't been able to tie that down to a particular fuel being in use. I will try to be a bit more systematic about observing engine behaviour and fuel economy and report back if I can see a real pattern. I get the feeling that even within brands you can get quite a lot of variation in quality from different outlets at different times, if so that doesn't make it any easier to be scientific about it.

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  • 10 months later...

Some advice for the carbon worries.

All cars get carbon build up on their throttle bodies, it is because of the exhaust gas reciculator valve and the usage of the crank case vapour in the combustion chamber. The throttle body connects the air filter line(tube) to the inlet manifold. But attached to this is a rebreather that introduces the crank case gases to the inlet. The carbon collects around the circumfrance of the throttle body, when you take the inlet pipe off it might look clean and nice, but take the throttle body off completely and look at from the back, you should be able to see light between the housing and the butterfly valve. When this is clogged up the ideling is affected because the ECU has to open and close the vale continously to allow the engine to breath. The job is simple to do, just need the right tools and some throttle body cleaner, carb cleaner is to aggresive. When the piece is removed beware, you will lose some coolant, yes the engine has coolant flowing through the throttle body, it is to keep the ideling smooth and the metal at a constant temprature. After you have cleaned and replaced the throttle body the ideling wil be high, around 2200 rpm, don´t take the car to the shop saying it is busted, the ECU will addapt the ideling to the new flow of air, the engine can breathe again. Drive it around for a couple of hours and repeat the next day, the computer needs both hot and cold readings to reset it´s fueling. If however after three days it still runs like a meth head, take it to the shop and tell them what was done to the car. The ECU might just need some direction. I am sure that somewhere on youtube is video detailing how do all this. I did it because my car was heavy on fuel and idled like a pig. REMEMBER NOT TO STICK YOUR FINGERS IN THE THROTTLE BODY UNLESS IT IS DISCONNECTED FROM THE ELETRONICS, YOU WILL LOSE YOUR DIGETS.

Hope this helps. if you do not know how to do this, get some expert help or some one is competent.

PS. my car is an Avensis 2.0 vvt-i 1Az-FSE automatic direct injection petrol 2003 model. 108430 km. The above job reduced my fuel consumption aswell.

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  • 1 year later...

Hi everyone,

Am a new member in your club. I happen to have a 2009 Toyota RAV4 which I have had for the last 4 months. I am from Kenya en I love this car very much.

My issue is that when am on the highway after the bump the car tends to stall does not pick immediately. After 30sec it shots like an arrow.

Took it to the mechanic en adviced me that the manifold might be blocked with carbon.

Remedy was to rmove the staff in the manifold, looks like a honey comb.

For sure the car gained its power. But then I was not yet out of the woods. The car started to back fire en the back tail started to have accumulation of sute/carbon, a sign of "RICH" Fuel injected.

Consumption has gone up.

Any one with an idea what might have happened.


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