thunderstruck507

iTrader: (18)

So I've been fighting through the idle tuning off and on for a couple months and I can get the car running great, park it for a few days and be back to square one.

If I adjust the set screw it will start running again, normally most of the time and then idle high sometimes. Eventually going back to where when I let off the throttle it dies almost instantly like it's choked for air bad. Flashing a new tune will not fix it when it's doing this which makes me think it's a physical problem.


I am starting to question whether the IAC could be hanging in the bore sometimes and not operating smoothly. I know people have had trouble with the blades on the old 90mm TB and was curious if anyone has had anything like this before? It's a new theory so I want to do some logs and watch IAC counts to see if they are changing like they should.

Thinking about taking the IAC out and cleaning the bore, checking for burs, maybe sand it lightly, and grease the IAC before putting it back. Just curious if anyone has heard of anything like this before.

Z28SteveA4

iTrader: (16)

i've never really heard of anything like that before with the 90mm but you never know. Pole it out like you were saying and check to see if there are any burrs. If you dont see anything then i would sand anything down. It honestly sounds like a bad iac to me. Have you changed the iac motor yet?

thunderstruck507

iTrader: (18)

yes, it's only a couple months old

thunderstruck507

iTrader: (18)

here is a thread detailing this problem for future reference

https://ls1tech.com/forums/pcm-diagn...pics-info.html

studderin

iTrader: (28)

ya. I was going to say to port it. It also helps with the air shear sounds on "cold" starts, when the valve is WO. Sounds like when a port goes unhappy on the flow bench, same thing. My SUX2BU is sealed to the outside open so winter cold starts is is LOUD like a jet, and people always ask about it.
this was with it ported, lol its a NW I havnt measuer the hole ID size, but its still a sqare 90* corner in the bottem of the IAC well and into the TB bore front and back.


edit, youtube vids 7 years ago. hahaha

thunderstruck507

iTrader: (18)

I started it up twice yesterday when it was below 40* and both times it fired right off and idled at my commanded RPM (tune is set to idle 1300 dead cold and drop from there in increments to 850 at around 130*).

Before if I touched the throttle I would have to extremely slowly let off the throttle or it would die. Now I can blip the throttle and it will fall down to 500rpm or so but then recover and idle.

Going to go back and port it some more including the internal passage as noted in the other thread. Then I guess I will have to go back and redo all the handicaps I put in the tune trying to get this thing to work.

My big clue was when we cammed my roommates car and his took me 1 try and minimal adjustments to get his to fire and idle perfectly with the ls6 intake and stock TB. I have many many many hours in idle adjustments (air, fuel, timing, etc) trying to make mine work and the Fast intake and TB are the primary difference in setups.