Recently we got a nice 2005 Toyota Vitz RS (NCP91) with a manual transmission.
It is great car in all aspects except power delivery and throttle response is pathetic.
We already have 1NZ-FE powered car in the family – Toyota IST and unlike the Vitz RS it is not that pathetic (in fact it is kind of fun to drive).
Yes, I have driven multiple Vitz RS and they were all asthmatic.
So what is so different between IST and RS? IST happens to have cable driven throttle, while RS has drive-by-wire.
Here is where Toyota screwed up and completely ruined the car: they made throttle map to emulate steam roller.
If I was Toyota I would not stick RS badge on the car, it is not a hot hatch simply because it lacks in engine department. Vitz RS should have came out with 1ZZFE at least.
What is even worse they decided to stick this anaemic throttle map on top. As if the car was not boring enough.
After consulting google and various forums I had two minor mod options:
1) Stick a throttle controller
2) Stick a throttle body off 1ZZFE.
I decided to go for second option as it is transparent from end user point of view. There are a few minor hurdles with this mod.
For one using 1ZZFE throttle body produces CEL/logged error. This is fixed by swapping control boards from 1NZFE to 1ZZFE body.
Second hurdle is that the coolant pipes are at different angle. I addressed this by sticking screwdriver and rotating outlet port to desired angle (it is press-fit).
Third hurdle is that the inlet rubber hose is a bit too small to fit 1ZZFE throttle body. This is rectified by dab of grease and brute force.
Forth hurdle is that 1ZZFE throttle body outlet is a bit larger than the intake manifold inlet. I haven’t yet addressed it. I plan to get a thin (4-5mm) plate made up with a slope gradually joining two diameters (the diameter difference is about 10mm, thus the lip will have 45 degree slope). Another alternative fix is to get another manifold and grind out the hole to the 1ZZFE diameter (while epoxy-ing and flattening surface to accept regular gasket). This option is a bit extreme.
The result was significant. The throttle response was as if it was cable driven. It is like going from I mode to S# mode on an WRX STI. It also lost the power gap after 5k, the engine revved more freely right through to red line.
Going from 1NZFE to 1ZZFE gains about 9mm at the front.
Going from 1NZFE to 1ZZFE gains* about 10mm at the back.
* Not true: as the inlet manifold sized at 46mm ID. This will need to be addressed somehow.
Note: the manifold has 46mm opening, matching the original throttle body.
This creates a problem that will have to be addressed in future – the step is visible here:
It appears that even with partial coverage of O-ring there weren’t any vacuum leaks (yet ;)).
In conclusion the overall result is great, the engine became more lively. Of course actual performance gain is probably minimal, but at least the car no longer has Tiida dynamics.
I used to be a fan of Toyotas when they made things like Starlet GT, Corolla GT etc, ie actual hot hatches. Vitz RS is not a hot hatch. Now Toyota is only making boring appliances, which is a shame.