Ok here's an update:
Aside from cleaning/swapping parts that I described in my last post I also pulled another set of codes after having the batt. disconnected for a couple hours. I got 543 in KOEO on demand, NOT memory. The fuel pump is definitely working (though noisy) so I replaced the front 02 sensor as I also had 02 sensor codes in memory from yesterday (did a search, found that 02's could be connected to a 543). Ran KOEO again and nothing, all 111.
Now for the strange part. Yesterday I could not pull the KOER codes; Everything would work fine up to the goose test but after that I'd get no CE flashes at all and after a minute or so a cylinder would drop, stay out for about 20 seconds then come back on like it was running a balance test. Now today I tried the KOER test and damn if it didn't work just as it was supposed to. Only pulled 2 codes, 412 & 413 which seem to indicate a bad IAC. I cleaned the heck out of it today but it didn't make any difference at all. I also ran a cylinder balance test; everything came back ok. Of course during the whole test the engine never ran over 800 RPM's save for the goose part of the test. Usually the engine runs up to 1300-1500. Same for the balance test...idled around 800, dropped to 500 when a cylinder was cut. shrug
Finally, I noticed quite a bit of intake resonnance...I'm not sure if people understand what I mean by that but it sounds like medium-pitched hum that one may hear from a wind instrument like a tenor saxaphone. My Contour used to make a similar noise, but I've never heard it on a SHO before. It's definitely in the intake manifold somewhere as it became MUCH louder when I removed the intake tube from the throttle body, and shortly afterwards the car stalled. Could this indicate a vaccum leak in the intake somewhere?
So to recap, here's what I have:
No idle condition when cold. Car starts right up but unless I give it some gas it will just shut right back down.
Low idle condition when warm, approximately 500-700 RPMS. It doesn't fluctuate up and down, sometimes it will idle higher up and sometimes down low; I guess it all depends on what intersection I stop at shrug
I THOUGHT I may have a computer problem since the KOER test would not complete itself yesterday, but today it worked just fine. CE light comes on when the ignition is turned on; relays, fans and fuel pump all seem to cycle normally. I thought the idle problem may be computer related but since it's working ok now and I still have an idle prob I must assume the problem lies elsewhere.
There's quite a bit of intake resonnance that would seem to be originating in the intake manifold itself.
Car runs great aside from the idle...no hesitation, secondaries hit like they should, car pulls strong.
I did have a CE light on occasion yesterday during the 2 hour drive home. Just a light, no noticable change in performance. Averaged 24.9 MPG, 100% highway miles.
I've cleaned the IAC, TB, EGR, swapped the MAF and TPS, replaced front O2 sensor, tried to reset the idle per the published procedure, cussed a lot, drank a lot, etc. Tomorrow I'm going to try a new IAC as well as a new fuel filter, but any and all advice is still appreciated!
