ECM fault?

[Dave Zug]

Having read most of the posts and responces, my advice is to revisit 
the things you say "arent" the problem. vacuum leak, contaminated o2 
sensor and sticking.clogged IAC come to mind. go back to the item you 
LAST CHANGED just before the problems occured. maybe a contaminated 
o2 sensor from coolant ingestion or from an in-tank additive or even 
a simple choke cleaning (throttlebody cleaning) or from oiling your 
K&N (although I have never heard of KnN oil doing anything bad.  when 
you go thru the GM procedures - everything always comes down to "go 
over the entire harness" after exhausting all other procedures.

I'm going to reveal my last bugger of a troubleshooting item, which I 
hope helps someone as much as it is embarrasing to admit my solution: 
I replaced the runners on my TPI 350 with a popular "large tube" set 
in preperation for a new bottom end later. the idle looped severely 
and when it stopped looping it ran at 1600+ rpm. the exhaust was 
really HOT, indicating LEAN. the o2 backed it up until it got burned 
up (yea, a cheap one.. i'll take the "GM GENUINE" advice thanks). 
come to find out that one bank of runners were skewed and I had a VAC 
leak. found it by spraying carb cleaner on specific spots underhood. 
it went away when the car was warm due to expansion I bet. with that 
fixed and a replacement in the mail, I still had high idle. Turns out 
when I cleaned the IAC and throttlebody out, the base passage setting 
on the TB was too large and had to be closed a bit. now perfect idle. 
I still wonder why I had to turn it down so much but spraying causes 
no engine reaction now, so no VAC leaks.  

Moral of the story is to remember EVERYTHING that changed when 
diagnosing.. even a little wipe of a throttle plate can get you. I 
too was ready to take the heads off and look for the bolt I thought I 
dropped into the intake ;-{

~~~
Dave Z. www.delanet.com/~tgp