Interesting IAC learnings
I've had a cold start problem on the Zilla for quite some time. Probably over 6 months. A month or so ago, I swapped a different IAC in (I have 3 spares) and it made no difference.
I chalked it up to the ported heads, rockers, etc, and the fact that the ICM rattles the injectors for the first 400 rpm'* before the PCM can take over. Maybe the ICM (which can't learn) doesn't know what to do with my bastardized setup.
I know I was running lean on startup. Wideband O2 tells me that every day, and after the 6th or 7th start attempt, it settles in to the proper AFR. So what if I block off part of the IAC passage? That'* a though that occurred to me.
I had a good 'winter opportunity' today, as I'd organized my garage for the engine swap, and only had to move my engine stand and engine hoist out of the way to install the new DVD deck in the SLE. Later (just a bit ago) I took that opportunity to pull the Zilla in and look into the feasibility of blocking off part of the IAC passage to help start the lean start issues.
I decided instead to compare IAC'*. Call it pin ABCD from left to right as installed in the TB, looking at the front of the car.
A-B was 48 ohms on all three spares. C-D was the same. On ALL THREE spares.
On the Zilla, A-B was 52 ohms, and C-D was 53. So I hooked up one of my spares to the harness, and cycled the ignition. Damn thing ejected the plunger and spring. They launched all the way to my alternator. Tried another, and it did the same thing. Must be normal sez me.
So I screwed one back in, and carefully aligned the grooves and notches, then installed it in a spare TB, put the screws in, and cycled the ignition a few times. It went back together ok, but was extended farther than the one that just came out. Ok, sez me, that'* what I want. Less air.
I installed it in the Zilla, and it wouldn't start. Fully closed. So I cracked the throttle with my foot a bit, started right up, then feathered the throttle down until the IAC took over and maintained my AFR and idle.
Tomorrow I get to find out how a cold start does. My gut tells me (I hope) that the IAC in the Zilla has been going bad, and that the replacement a month or so ago hadn't had time to 'learn' before I gave up and swapped back, writing it off to a bastardized setup.
I'll let you know tomorrow if there'* a lesson to be learned here.