High Idle RPM Solved

After installing a custom IACV blockoff plate a few weeks ago, i managed to lower my 4A-GE idle speed from 1500 to 1100 RPM. This is with the idle screw set to max, meaning there's no air coming from the idle air passage. It's still a bit too high as according to the manual, it should be around 850 RPM. Last weekend i went to check further on this problem.

Since the idle screw has been maxed, this can only mean that there's a vacuum leak somewhere on the intake manifold. Hoping that it wasn't the throttle plate needing to be replaced, i went to check the vacuum lines around the manifold. Here's how the lines look when i checked.

Keep in mind that my intake plenum was cut-n-shut to relocate the throttle body to the other side as it was for FWD originally. Notice anything wrong?

See where the PCV line from the cam cover goes? This is obviously wrong. Connecting it this way would always leak vacuum from the cam cover to the intake. Also notice the brake booster vacuum line goes to the inlet near the cold start injector. Originally, this was where the PCV line supposed to connect. I find this also suspicious. Not in a way that it would leak vacuum, but exactly the other way around, it might not even have vacuum. Originally, that inlet has an air passage that goes to the throttle body and channeled out to just before the throttle plate, like so..

With an aluminum plate now in place of where the TB was, this hole might be blocked. Well, you tend to start doubting your engine swap workshop's capability if you find out that they connected the PCV line that way. It was easy to check if they made a channel on the aluminum plate so that vacuum remains. Run the engine, unplug the brake booster line, check for vacuum using your finger. Vacuum's there. Good, they didn't screw up there, at least. I then just need to take the PCV line off the intake runner.

Taking the PCV line off means that i need to get some form of oil container. Commonly known as oil catch tank, this ensures that oil coming out from the PCV line won't mess the engine bay. Failing to find any container to use, i temporarily wrapped it with sponge. My friend Stanley used an aluminum water bottle, didn't you Stan? I think i'll be following your steps soon. With the PCV line off the intake runner, I decided to move the brake booster vacuum line there, hoping it would make bigger vacuum so that it helps on braking with those 4-pot RX7 calipers. Hence, it was the vacuum inlet on the intake plenum that needed to be plugged. I used a braided rubber hose and plugged it with whatever my hands could reach that time, which turned out to be a ziptie and 12mm bolt. Another ziptie to secure the brake vacuum line in place and here's the final result.

Loosen the idle screw a bit, crank the engine, check the idle RPM, adjust the idle screw and there you go, i'm idling at 850 RPM now! Idle speed adjusting screw is now working and I'm really glad vacuum wasn't leaking from my throttle plate. It would be more difficult to solve obviously!