Is that a common mod to do that? It seems to me that the seats relationship with the threads are pretty important, meaning the if the center line of the IAC threads and the center line of seat are much different it will not "seal". I would assume that the factory specs are way beyond what a hand drill is capable of. I would assume you would need a milling machine. Also the finish on the seat would be important. If the IAC can not seal or home correctly because of the seat is miss-aliened or leaking air it could cause erratic behavior.

 

Sorry for the late response. I just finished replacing my PVC system with new lines. The idle problem is definitely much better 75% of the time now, but it still does it once in a while. When it happens the RPMS sit around 2000 RPM when I'm coasting in neutral/clutch until I come to a complete stop. Then the idle fluctuates up and down from 800-1100 RPM.

I did drill the IAC hole out bigger but not much of a difference. The biggest difference was from fixing the vacuum lines, although it didn't fix the issue.

I initially did the port and polish as people said they have much better throttle response and "seat of the pants" feel. I cant vouch for the port and polish alone because at the same time I modified my stock air lid in which I felt a major difference in throttle response and "seat of the pants" feel in the upper RPM. 5th and 6th also seem to be more usable.

You cover the ports and drill them out because if you look at the stock design, there is a large area that creates turbulence, this smooths out that area and just allows air to the ports. You can google it to see what I mean.

I found needle bearings on my oil drain plug now, so while I'm in there I'm going to replace the valve cover gaskets and the intake cover gasket just to eliminate all possible air leaks.

I'll give an update once I've made more progress.

 

It's a fairly common mod, google "how to port and polish ls1 throttle body".
I see what you mean about making it seal, but that part of the throttle body is not touched during the mod. The only difference is filling in a turbulent area and drilling the holes back out. It shouldn't have any affect other than better air flow.

LS1 Throttle Body Port and Polish Instructions

 

Im still a newbie here but when I cleaned by TB and removed the IAC and TPS I had issues with the TPS for a while since it had to reset itself. I had to learn the hard way when my car was trying to cut off at idle in traffic lol. Hopefully that's all it is

 

are you getting readings from the tps yet.

 

I was actually thinking that. I reset the TPS and IAC as well as the PCM last week, so it's possible it's still doing a relearn.
It's totally fine 75% of the time now, so it's a weird one. I wouldn't doubt that it had something to do with the vac leak because it was much worse before i fixed the leaks.
I have another intake gasket on the way to completely eliminate any vacuum issues.

As for the TPS readings, the multi meter was pretty well on par with the voltages fully open and fully closed. Something like .54v when closed and 4.65V when open.
On my scanner I can only get TPS readings from the MAP, nothing showing up for the TPS sensor itself.

 

you still getting codes?

 

Funny you ask as my CEL just went on this morning. My reader is at a friends house, I'll check it out tomorrow when I get it back. I was getting IAC and TPS codes, but I think thats from unplugging them to reset. Ill update as soon as I can.

 

No more IAC or TPS codes so far, the problem has only came back twice in the past 3 weeks of daily driving.
It only does it when the car is at operating temperature and I turn it off and turn it back on. It will never do it on the first ignition cycle, only if I have to make one or more stops. It does not fluctuate near as bad as it did either, only 100rpm or so.
It happened last week when I stopped for groceries, so I turned the car off for a minute and back on and it went away.
Such a weird problem but at least it rarely happens now.

 

have you had it tuned yet. might be a good idea to at a place like PCM for Less or better yet solomon at LT1 PCM Tuning - Welcome!