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TL;DR version (16/05/2018): Apart from an oxygen sensor failure (A failure not specific to D4 motors), I have yet to notice any issues with the D4 1AZ-FSE fitted to my Avensis @190,000 km. Running it on 98 octane in my own experience did not net any economy nor performance gains over and above 95 Octane (In fact, there was consistently a Loss of mileage over 95 octane). Original post below...

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It seems the opinion on this forum is "Avoid the D4 engine" (perhaps like the plague). Apart from some commentators on Africa sites, it seems pretty much only the NZ AA is the only other entity I've seen routinely bagging this engine. From what I gather, even the NZ New 2003-2008 Toyota Avensis GX all have this D4 1AZ-FSE engine in them as well and if I'm not mistaken, only the lower spec'd GL has a non-D4 1800cc VVTi engine. The comments here have naturally left me concerned.

Shortly after I got the car I read here that it was probably best to fill it the highest octane as possible so I put BP Ultimate 98 RON for three consecutive tank fulls and unfortunately, my car I have to say ran comparatively poorly. More vibration at idle, Growling / rumbling when cruising at lower Revs, (1300-1500), distinctly rougher acceleration with 10% INCREASE in fuel consumption to boot (All 3 tank fulls). Having had enough of that, started filling the car instead with Z Energy ZX Premium and Caltex Techron Premium (Both 95 RON) and it made the engine run a lot more normally and smoothly with better mileage to boot.

Regardless, is the problems with this engine mostly centered around carbon build up? If so, can't a suitably experienced mechanic take the intake manifold off and give the valves a clean out as part of the routine maintenance regime at periodic intervals? Can't this be done ourselves if given the proper instruction? What about running "upper engine cleaner" through the intake every now and again?

Also, while we're on the subject of DI engines, I note Caltex's site claim that their Techron "formulation" somehow cleans the valves of Gasoline direct injection engines... Not sure how true this is though as I understand that the fuel never touches the backside of these intake valves on Gasoline Direct Injection engines?

At the moment, my car is still problem free (the only complaint is that it doesn't coast as well as my 1996 vti Honda Accord). Anyway, More and more of these Petrol direct injection engines it seems are appearing on the market, Including new cars with SkyActiv and SIDI, and it seems there are the odd reports already that some owners of such vehicles are also experiencing this carbon build up?

Pleased to hear your car is running well - we're happy if you're happy.
However, we don't pick on engines to run down out of the blue. Our apprehension regarding the Toyota D4 and Mitsubishi GDi engines is based on experience.
I'm surprised you had running and fuel consumption problems on 98 octane fuel that disappeared when you reverted to 95, but I guess if this was your experience, you should do what works best for you.
Unfortunately, no matter what type of engine cleaners or other products you run, these won't help the problem with these engines as the issue is with running exhaust gasses back through the intake and by this stage any additives have been burnt off and will not help to reduce carbon emissions from the exhaust.
Yes, you could remove the manifold and perhaps the cylinder head to clean out carbon deposits, but as you can appreciate, this is a very big job and the cost of performing such a major operation as routine maintenance can't be justified.

Many thanks Andrew for your reply. Much appreciated.

For now the engine is running well (that is), but short of going through the hassle of offloading the car while it's still running well and getting something else, I am wondering what can be done to minimize the chance of encountering future problems with this engine if it's allegedly as bad as it is? I keep hearing the terms "Catch Cans" and "EGR delete kits" mentioned around the place as methods to reduce carbon deposits (but mostly on turbocharged vehicles which the Avensis is not). Does anyone here have any experienced of these, if so what are you thoughts?

So even running some sort of Upper engine cleaner (Not talking about fuel additives here) every now and again directly through the air intake / vacuum hose is perhaps ineffective at keep carbon deposits levels down?

Cheers,

On some early direct injected engines it was possible to block off the EGR system, however on later models (and I suspect your Avensis falls into this category), engine management systems try to compensate for mixture and emission readings which are outside of normal parameters and you end up with poor running, excessive fuel consumption and high emissions. Therefore, it's not a viable option.
You are quite correct that there aren't really any cleaners that can effectively keep carbon deposits down.

More FYI only. As of Today (2018-01-14)...

Apart from an Oxygen sensor failure about a year ago, I haven't noticed any issues or otherwise symptoms of carbon build up with the engine in this vehicle at 186,000 kms. Car has had the usual regular servicing (Oil / filter changes, brakes and other wear items where needed) every 6 months.

Have primarily ran it on Caltex, Mobil and Z 95 Octane. Have tried a few further consecutive runs with 98 Octane from BP and Mobil, but did not discover any power or fuel economy improvements on any of the tests over and above running it on 95 Octane fuel.

Hi there,

It seems after reading about the D4 VVTI engine, our 2004 Toyota Avensis (200km) is possibly experiencing some of the issues discussed in the forum with carbon-build up.

The car seems to run fine, but over the last six months it has developed a 'whirling' sound - best described as the sound made when paper hits a fan. To my knowledge the sound is constant when over 1200 rpms. I have had a listen and a play around when the bonnet is up and from what I can see, its not a loose mount or heat-shield and it seems more internal when you are driving if that makes sense, which is why I am leaning towards the carbon build-up. The car been run on high-octance since we purchased and has had regular maintenance in the 5-6 years we've owned it, (these issues have never been bought to my attention either) but to keep costs down in last year, I've done the basic service stuff myself (oil/oil filter change and top-up and air filter.)

Firstly, I was wondering, is cleaning the valves and cylinder head a major job that any mechanic can undertake or is it more of a specialist activity?

Secondly, I am not a car person, so what happens if this particular issue isn't solved? Does it just affect performance, economy etc or does the engine eventually seize up.

Thanks in advance