smitty2919

OK so call me stupid, but when doing this mod, i understand the whole idea of making it and drilling holes for the bolts.

but the stock one has 2 large holes, when you make the new one do you make one large hole and on 3/16" hole?

or do you make just one 3/16" hole?

i did this because of the haning idle with my PP 75mm tb and plenum.

i made a gasket with 2 bolt holes and a 3/16" hole for the IAC and now it sits at 1000rpm for an idle.

i read the directions on the sticky, but maybe im dumb for how many holes to make lol

thanks
Dean

Z28KLR

I think in the replies to that sticky there were some who had to make the hole a little larger than 3/16" to get a good idle. A few people tried it and didn't like the results or had issues with the engine stalling, so depending on your mods it may or may not work for you. Just one hole for the mod. I still gotta try this one myself.

smitty2919

thanks for the reply, yea the 3/16" hole worked great for kicking the revs down but like i said it gave me a 1000rpm idle. mine is a little larger than 1/4" but havent driven it yet, but at least my idle is correct now

cliffyk

The IAC body casting and the gasket are "universal" in nature, in that the casting can be machined to behave as a bypass, or plumbed air valve. If you examine the plenum side of the IAC casting on our cars (machined to be a plumbed unit), and the upper plenum, you will see that the recess nearest the throttle body has no hole into the IAC--nor does the plenum have a hole on that side.

The OEM gasket has to holes to work with either IAC style, but only one is used--when making a new gasket you only need to cut one opening.

All this said, a much easier way to make an IAC restrictor is to drill a hole in a 1/2" copper pipe cap and stick the cap into the IAC feed hose. I have small machine shop and made an insert of aluminum bar stock (see below), but the copper pipe cap will work just as well...



BTW--I ended up with a 0.290" bore, about 9/32"

Blk003GT

whats the benifit to doing it the way u did it cliffy. btw ive been running the way the OP is doing it for about a year now.

cliffyk

None, other than that drilling a hole in a pipe cap is easier than making a custom gasket or gasket shaped plate--it's also easier to remove and replace when playing with different orifice sizes...

MU71L4710N

yeah if u fully read the sticky you may have to make the hole smaller or larger. no 2 cars act the same with the IAC mod. ontop of that some cars just do not like any modding to the IAC and won't idle with a hole any smaller than stock. my car was one of those. my car would almost die with the 3/16 hole and RPM dropped WAY too fast to make driving (manual) easy, it was a challenge. so i enlarged the hole to like 5/16 and RPM hang was good but idle sucked, so i had to enlarge the hole a little more and it acted the same way that it did with stock size so i put the stock gasket back in and said forget it.

smitty2919

thats where i am right now, i just got done putting the stock gasket back in there. when coming to a stop the car would not kick down lower than 1000rpm and that was more annoying than a little idle hang while shifting.

IF it worked correctly and i could get rid of the hang AND my normal idle i would have left it in. but maybe ill play around more tomorrow.

anyone know why when i had a smaller hole the idle would be higher and the bigger you get, the lower the idle?

best way to solve a problem is to understand it first...

thanks

cliffyk

When you first installed, and when you modified, the restrictor did you disconnect the battery for 5-7 minutes? Doing so clears the KAM (Keep Alive Memory) and forces the PCM to relearn things such as long term fuel trims, and idle air trim...

The PCM does all it can, via the IAC, to keep the idle at the speed set in the tune. It does this by adjusting the duty cycle of a signal sent to the IAC, controlling how much air bypasses the throttle. A number of factors are involved in setting this duty cycle (IAT and ECT mostly) and the PCM stores values for particular circumstances in the KAM, constantly modifying them as it learns more about the engine.

Resetting the KAM makes it relearn these values NOW, and should it be done anytime you make significant changes to the intake tract--like restricting the IAC flow.

smitty2919

yep i did the undo the battery when i first used a 3/16" hole but got a 1000 rpm idle. i didn't drive the car far. so unless i should have driven it more to see if it would sort itself out.

if i end up doing it again ill make sure to drive it more. the idle hang isnt THAT annoying to me. i see what people are talking about but its not a huge deal to me(maybe because mine isn't that bad)