Base idle question

[reklipz]

Assume the car is hot off the dealer lot and everything works as designed. Assume the engine is idling at operating temperature.

1) Disconnect the IACV electrical plug.
2) Completely cover/plug the two air bypass inlet holes on the inside wall of the throttle body.

Does the engine stall?

What does your car do? On my car, the engine does not stall. In fact, it idles at ~500 RPM. Does this mean I have a vacuum leak?

[GhostAccord]

No that means that you are @ base idle. When you unplugging the IACV that should close the valve. And once the engine is up to temp the FITV should be pretty much closed as well. There really shouldn't be much air flowing through those ports, if any.

[reklipz]

That's my point though: there is zero air flowing through them when covered/plugged. All of the other valves are closed as well, so there is no air running through them. The bottom bypass inlet feeds the IACV, and the top feeds the base idle set screw mechanism, and they may also feed the FITV and ABV (both of which should be closed anyway, mind you).

So, when I plug those two bypass inlets, there should be no air getting to the engine, right? Unless some air is supposed to come in via one of the various vacuum hoses, how is the engine not stalling out? Basically, if I plug the whole throttle body inlet, the engine should stall, right?

[GhostAccord]

The upper port is for the IACV, the lower port is for the FITV, plugging those shouldn't stall the car. The idle adjustment port is located inside the TB on the top just in front of the throttle plate. It is not connected to the IACV or FITV ports. Also IIRC the throttle plate itself isn't completely 100% closed. In order to stall out the car you would have to completely close off the idle adjustment screw, the IACV and FITV ports and put something over the throttle body opening.

If it doesn't stall out then, you have a pretty big vacuum leak.

[reklipz]

Perhaps I should make a video...

Anyway, I can assure you that the bottom bypass inlet on the F22Ax throttle body feeds the IACV. As well, the air flow that the idle adjust screw alters is fed by the top bypass inlet on the F22Ax throttle body. And again, by bypass inlets, I mean the holes that are located inside the throttle body, feeding from the front of the throttle plate to the various ports for the valves and the idle screw. Blocking these two inlets is essentially the same as blocking the main throttle body inlet, with the exception of any slip past the throttle plate (which should be extremely minimal). I believe the throttle plate (at operating temperature)should just touch the TB wall, but it should not be wedged and free to move. I'm not sure which inlet feeds the FITV, but I would guess it's the bottom one as well, though perhaps not. The air boost valve appears to be fed from one of these inlets as well.

[GhostAccord]

Yes sir you are right I forgot that the F22A is opposite a lot of other TB setups with everything mounted to the front of the intake it changes everything.

So what are you trying to figure out? Are you having some sort of idle surge or high idle issue. Because with the IACV unplugged and the engine up to operating temp you should be seeing 550 ±50 RPM.

[reklipz]

I think I have an intake leak somewhere, or I don't understand how the system works. I either want to fix the leak, or actually understand what's going on. I think the answer to both is the same, so it's a win-win.

I would expect that when I plug those two bypass inlets the engine will stall. It did not stall, and in fact, blocking the inlets didn't seem to phase the base idle in the least (which is at ~550, with the idle set screw bottomed out). Now, a constant non-wavering air leak is in effect the same as increasing the lower limit of the idle set screw, so if you can get the idle to spec this way, then there is no real difference with the exception that the leaking air might not be filtered.

[dj_ender]

Ok, so are you removing the intake tube and plugging just the holes? Because as GhostAccord stated, theres another hole that feeds the throttle screw, up the top of the TB, just before the throttle plate. What happens if you just cover the entire TB with your hand? If it doesnt stall, you have a leak. If it stalls, thats normal.

[reklipz]

Ok, so are you removing the intake tube and plugging just the holes? Because as GhostAccord stated, theres another hole that feeds the throttle screw, up the top of the TB, just before the throttle plate. What happens if you just cover the entire TB with your hand? If it doesnt stall, you have a leak. If it stalls, thats normal.

I realized that I could simply cover the main throttle body inlet and achieve the same effect only after I finished up from removing the intake tube and plugging the holes.

However, I'm fairly certain that the idle air adjust screw is fed by that top bypass inlet; adjusting the screw adjusts the amount of air taken in through this inlet. As well, I have an H23 throttle body that works the same way (top inlet feeds idle air adjust screw, IACV and ABV, and bottom inlet feeds the FITV).

I will try covering the main throttle body inlet tonight and see if it stalls, though I'm doubtful it will. I'm pretty sure I have an intake leak as described, but it seems I can just barely account for it by closing the idle air adjust screw completely. If someone else could replicate these tests on their known good system, I would be more than grateful.

Other than those two bypass inlets, the only other places air could leak past is one of the various vacuum lines (which have all been replaced) or its attatched accessory, or the PCV or EGR systems.

[reklipz]

The upper port is for the IACV, the lower port is for the FITV, plugging those shouldn't stall the car. The idle adjustment port is located inside the TB on the top just in front of the throttle plate. It is not connected to the IACV or FITV ports. Also IIRC the throttle plate itself isn't completely 100% closed. In order to stall out the car you would have to completely close off the idle adjustment screw, the IACV and FITV ports and put something over the throttle body opening.
If it doesn't stall out then, you have a pretty big vacuum leak.

Ok, so are you removing the intake tube and plugging just the holes? Because as GhostAccord stated, theres another hole that feeds the throttle screw, up the top of the TB, just before the throttle plate. What happens if you just cover the entire TB with your hand? If it doesnt stall, you have a leak. If it stalls, thats normal.

It stalled. The gap on the throttle plate is much more than I had remembered from two years prior. Thank you all!

[GhostAccord]

At least now you know.