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 onestopcuttingshop.co.nz for water cutting.
The plate is 8mm thick. The onestopcuttingshop.co.nz supplied the aluminium, total cost was just under $60 (NZD) including shipping.
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.
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.
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.