I'm having trouble getting idle down where it should be. Fully warmed up (195*F), IAC pretty much stays at 40. TPS is at 0.56 or so. When I set the rpm down to around 700-750, the throttle plates are pretty much closed and tend to stick coming open, and they don't want to fully seat without help. Which means that it lurches off idle as the throttle finally comes loose, and any time I let off the throttle smoothly, I get an idle around 1000+ TPS is showing the throttle not closed.

This is a 7747 with a basically stock (for now) akaj bin (88 K5 Blazer 350 TBI w 700R4).

Several questions:

The reason I posted in here; I noticed in my bin has an "IAC vs Temp" table. The Y axis is labeled as "Deg C", is that correct? If it's actually "coolant temp counts" then "49" puts me at 195*F and the table shows "40 IAC counts" which makes sense. So, just to experiment, I modified the table to put IAC counts at "49" to 20, and smoothed the curve going up to colder temps and tried again. Same thing, 40 IAC when heated up...



Obviously I don't understand the IAC vs Temp table usage, or I'm missing something else. I'm going to try the "A+B" min air adjust series again to see if it makes a difference this time, haven't tried it since the new chip, but I'm clutching at straws.

After that, I guess I'll pull out the TB, which is a bored out 46mm unit with aftermarket plates, and see if maybe they are not quite aligned with the bores which would at least (maybe) allow me to get the idle down low enough without sticking, but it sure seems I should be able to get the IAC on down below 40, which would fix everything I think...

Any ideas?

 

my bin is set at 0 steps at 185 deg F. TPS at idle is like .58V. that constant is the correct one to reduce your IAC steps. your throttle plates may be sticking in bore. i would look at throttle shaft as well. my old crossfire had same problem and was due to butterfly being not perfectly square in bore(2.00). i would disconnect the throttle cable and do by hand to see if it is TB related or cable//linkage related. even at 0 steps i cannot get idle under 850 but i am ok with that. no vac leaks BTW.

 

Thanks for the confirmation. My stock bin has 24 counts above something like 140*F or so. I guess I'll burn a new one with maybe 10 or something on the upper ranges, then swing up along the original curve at colder temps. I've seen some posts about making sure you stay above 0, but maybe I should come on down to 4 or 5 to improve the idle fuel atomization as much as possible.

I've already checked without throttle cable and it behaves the same. Looks like I will have to take out the TB again and see what can be done about the plates, bores, and perhaps the shaft. I've also got to figure out that low FP problem so I'll be checking the spring and diaphragm at the same time. Maybe this after noon...

 

Have you tried retarding the timing at idle?.
*Killing* some HP at idle would mean opening the throttle a little.

 

Hmm, never even occurred to me. I still haven't got my VE tables worked out, so I haven't even looked at changing the stock timing tables yet, but that just might do the trick if I can't get it settled in by tweaking the throttle plates. Would that also cause the IAC counts to go down? I read your (at least I think it was yours) post on all the things that go into IAC and don't begin to understand it yet. I know that opening the plates more should bring the IAC down, but it seems to stay at 40 no matter what I do, though I have seen it drop periodically driving around for no reason I could figure, even saw it ideling near 0 IAC a few times.