'93 LT1 IAC counts---what should they read and when?

[jay72]

Been reading a lot. My chip tuner said to close the throttle blades and get the IAC counts to 30-40. Also read several things online that say 30-40 is the sweet spot (in those exact words).

But when? Cold idle? Hot idle? I'm assuming any idle not in gear with the a/c off.

Seems I can get it to run right around 30-40 idle in park, but everywhere else it may go out of that range? Like hot with the a/c on and in drive it goes to 160 but idles fine. Is that ok?

So is setting the IAC counts to 30-40 only at idle, in park, a/c off? Any other IAC reading is normal as long as idle is ok and BLM's aren't split too bad?

[steveo]

short answer:

you generally want to close the throttle plates till they're almost binding in the bores, and drill your idle passage for a hot idle target of somewhere between 30 and 50 steps at hot idle in gear (which is the lowest point the IAC will see, barring a vacuum leak or something)

that allows the idle passages to work properly, indicates that not too much air is going past the throttle plates, and allows enough headroom for raising idle when cold or during throttle follower operations.

long answer:

a stable idle with lt1's intake plenum involves getting as much air through the idle passages as possible, and as little past the throttle plates.

the idle passages are a seperate set of air holes that attempt to flow evenly to all cylinders, to help get around the fact that the lt1 plenum at very low rpm causes uneven distribution of air and fuel.

there are two paths to the idle passages. one is via the idle control valve, the other is via the idle bypass hole.

the idea is to get as much air through the idle passages as possible, not necessarily just get the IAC counts high (but in general, higher is better, as long as it isnt' maxing out at high speed on a cold engine).

[jay72]

I appreciate the reply steveo.

After posting I started over. I drilled the TB hole .005 bigger, closed the throttle until it just touches the stop screw, reset the TPS to where it was.
The BLM's are getting very close to each other. The IAC counts are lowest of 37 at idle in park, and 88 at idle in gear (stock converter). The idle does switch 25 rpm lower than commanded so I guess I'll try to lower the IAC counts and increase idle by drilling the hole one more time.

With the a/c on it's a whole different story, it just commands 850 rpm, idles at 650 but slowly creeps up to maybe 750, the IAC's are at 160.
The annoying part is when I turn the a/c off the commanded idle stays at 850 rpm seems like until the car is shut off. During that time it idles too high.