Paul Workman
10-09-2010, 10:05 AM
A thread a while ago mentioned their LT5 "hunting" for idle speed after installing their Fidanza FW. Well...mine too. Tho the Fidanza might require some idle adjustment, due to the reduced rotational mass, it wouldn't cause my IAC counts to be ZERO (TPS voltage = .54, BTW)
In my case my plenum and IH gaskets are fresh and everything is freshly torqued w/ Locktite on the bolts. So, I could move on to the one area that has been neglected for some time...the throttle body.
I think I'm out of the woods, but here's some observations and a couple lingering questions:
I've read about some kind of sealant associated with the throttle plates - mine has none that I could see on either the primary plate or the big secondaries. Q: Vas es los!...(What goop???)
While holding the TB up to the light, I could see cracks of light around all 3 of the plates. It would take a wire gauge to measure the gap, but I would guess not much more than .001 (if that) where light was getting past. I also noticed what appeared to be a few grains of carbon or grit along the periphery of the secondaries - which I mention due to a phenomenon I observed later.
Pete suggested I turn the idle set screw in about 1/2 turn and see if that might help the hunting. W/ the TB in hand, that is easy enough to do - so I did.
After a good cleanup, a new set of Jerry's excellent gaskets replaced the cracked and brittle (almost like plastic!) ones that were on there.
Back together and fired her up. NO HUNTING! But, the IAC was at ZERO.:icon_scra The scanner was reading 675 rpm...but ZERO? Discussing that w/ Pete, he suggested that with the new idle screw setting it might be perfect for the idle speed I was observing w/o any help from the IAC - seems logical to me too. Nudging the rpm up with throttle and allowing it to fall back...counts drop to zero and idle is steady at 675. OK, it is idling fine now at 65* ambient air, but what happens at say 30*?
So, after talking w/ Pete, I cranked her again, only this time I "woofed it" a few times - enough to get the secondaries open. The idle returns to 675, but now the IAC is reading "14". Hmmmmm.....:icon_scra I woof it again and watch the IAC steps zoom up over 30-40 and then slide down to about 12 before recovering to rest again at a steady 14. Idle is smooth and 675 rpm.
Why are the IAC counts 14 now when it was ZERO initially? I reflect on the bits of dust or lint around the periphery of the secondary throttle plates and wonder if during the moments when the secondaries were open, did the foreign debris become exhaust gas and the secondaries now sealing better I wonder?
In any case, I like the IAC having at least SOME wiggle room. More later, if I haven't bored y'all to tears already!
P.
In my case my plenum and IH gaskets are fresh and everything is freshly torqued w/ Locktite on the bolts. So, I could move on to the one area that has been neglected for some time...the throttle body.
I think I'm out of the woods, but here's some observations and a couple lingering questions:
I've read about some kind of sealant associated with the throttle plates - mine has none that I could see on either the primary plate or the big secondaries. Q: Vas es los!...(What goop???)
While holding the TB up to the light, I could see cracks of light around all 3 of the plates. It would take a wire gauge to measure the gap, but I would guess not much more than .001 (if that) where light was getting past. I also noticed what appeared to be a few grains of carbon or grit along the periphery of the secondaries - which I mention due to a phenomenon I observed later.
Pete suggested I turn the idle set screw in about 1/2 turn and see if that might help the hunting. W/ the TB in hand, that is easy enough to do - so I did.
After a good cleanup, a new set of Jerry's excellent gaskets replaced the cracked and brittle (almost like plastic!) ones that were on there.
Back together and fired her up. NO HUNTING! But, the IAC was at ZERO.:icon_scra The scanner was reading 675 rpm...but ZERO? Discussing that w/ Pete, he suggested that with the new idle screw setting it might be perfect for the idle speed I was observing w/o any help from the IAC - seems logical to me too. Nudging the rpm up with throttle and allowing it to fall back...counts drop to zero and idle is steady at 675. OK, it is idling fine now at 65* ambient air, but what happens at say 30*?
So, after talking w/ Pete, I cranked her again, only this time I "woofed it" a few times - enough to get the secondaries open. The idle returns to 675, but now the IAC is reading "14". Hmmmmm.....:icon_scra I woof it again and watch the IAC steps zoom up over 30-40 and then slide down to about 12 before recovering to rest again at a steady 14. Idle is smooth and 675 rpm.
Why are the IAC counts 14 now when it was ZERO initially? I reflect on the bits of dust or lint around the periphery of the secondary throttle plates and wonder if during the moments when the secondaries were open, did the foreign debris become exhaust gas and the secondaries now sealing better I wonder?
In any case, I like the IAC having at least SOME wiggle room. More later, if I haven't bored y'all to tears already!
P.