Toyota Vitz RS throttle swap sorting out bugs

This is a follow up to this post.

After a few weeks of testing the throttle body swap the following issues have surfaced:

1) Very high idle on cold start up (>3000rpm)
2) Random idle oscillations (cold and warm start up)
3) Abrupt overrun transition

I suspected two things that could cause these issues.

1) Air leak due to improper seal between 56mm throttle opening and 46mm intake manifold (the throttle would only partially cover the O-ring)
2) The default opening of the throttle body was set too high (due to being set for 1.8L engine).

To remedy air leak issue I have ordered a water cut aluminium plate. I used for water cutting.
The plate is 8mm thick. The supplied the aluminium, total cost was just under $60 (NZD) including shipping.

Here are the files I made for water cutting:

To remedy the idle oscillations all I needed to do is to adjust default opening of the throttle. The adjustment screw is on “top” of the throttle sealed with epoxy resin.

Here is the received water cut plate:

I have marked out 55mm for filing in the tapper/funnel (slightly under 55.6mm of the 1ZZFE throttle opening):

Test fit the blank against the spare 1NZFE throttle body to ensure there is nothing interfering:

Hand filing throttle progress:

To make sure even finish I frequently rotated the plate in the vice and changed direction.

Test fit the filed plate:

Applied thin coat of sealant on one surface (between throttle body and the plate):

Note: there is no need to apply sealant between manifold and plate as I retained existing O-ring.

Checking for step, unfortunately there is still 1mm step, but I think it is close enough as hand filing is a very time consuming for such small thing:

Here is where the “idle” adjuster (not really idle adjusting but more of a starting position):

The adjuster screw mostly freed from epoxy (using a fine flat screwdriver as a pick):

Using 2mm Allen key I turned ~3 times in total counter clockwise to reduce default opening angle so the ECU would not overshoot on initial startup:

Best way to adjust this is to do it while the ignition is in OFF position, one turn at a time (or even half turn), starting the engine and checking max RPM: it should be below 2000 on warm engine and drop below 1000 couple of seconds after start.

This is what the plate looks like from outside:

Note: I left out two nuts between the coolant pipe bracket and throttle body, thus removing the need to replace the studs with longer.

As last thing I pulled out 7.5A ECU-B fuse for a few seconds to kick-off learning of the idle. I left it idling until it completely warmed up to give ECU plenty of time to learn.

At this stage this mod removed all the idle issues.

I will cover the adjustment screw with RTV once I am sure that oscillation are completely gone during the cold start.