1227748 refinement level?

[Nick]

So, I own an 88 fiero 2.5 (TBI DIS) with the 1227748 ECM.  Over 
the last few years I've come to recognize a few traits of the ECM 
which bug me.  Most of them are related to stupid idle tricks it 
plays from time to time.  (I'll explain those at the end of the email..)

My questions..  

What was the level of refinement back in the 80's on GM ECM's?  
Did "lowly" powertrains such as the 2.5 get ignored in favor of the 
more prestigious platforms?  And thus one could perhaps deduce 
that the PROM code isn't as good as i could be?  Or perhaps the 
whole ECM design?  It's an early P4 design.

GM used this ECM up until '92 in 2.5-powered vehicles, and I've 
thought about getting the related PROM, but my bottom line (right 
now) is that without the knowledge (and prom burner and 
associated hardware) i am probably asking for trouble.

Originally I had (don't quote me on these numbers, pulling from 
memory) ACMH9544, which I believe came with the car.  Recently 
I've run ATBS3453 which is the last GM-released PROM specific to 
my application.  No real improvements for the most part, other than 
elimination of an occassional obscenely high cold high idle of ~ 
2500 RPM.

Is there a "low-brainer" (as opposed to no-brainer) swap to a more 
modern, refined ECM that would have calibrations close enough to 
work with my 2.5 DIS 5-spd without hacking (which i'm not 
currently equipped or knowledgable enough to do?)

Oh, and for anyone who is curious.  By stupid idle tricks, I mean 
things like.. not being able to "catch" the idle fast enough when 
you suddenly let off the gas, causing the motor to stutter down to 
500rpm or so before the IAC can catch it and bring it back up to 
950-1000...Especially when cold.  I'm assuming this is becaues it 
steps the IAC to 0 when TPS > 0, and then steps it back out as 
TPS reapproaches 0, which I don't understand the logic of.

Not compensating for the additional alternator load when the 
radiator fan kicks in (idle stumbles down to 600rpm before IAC 
grabs it back up) even though the ECM is what triggers the radiator 
fan and it should know better.  At least it's smart enough to 
compensate for the A/C... seems lazy of the programmers to not 
reuse the step-up routine for the radiator fan too.

The code also will not reduce IAC steps from cold idle choke to hot 
idle unless VSS is 0, and even then it takes 10-15 seconds to fully 
step out the high idle.  Really annoying if it never gets the chance 
to step out the cold high idle before you get on the 
highway...sometimes I get right on the highway and drive for an 
hour, and when i get off the highway and pull up to the light, it will 
STILL be in high idle mode, having not stepped down to normal idle 
yet.  soon as I pull up to the light and come to a complete stop, 
the ECM noticably starts reducing IAC counts and brings the idle 
right down... I wish it would look at the CTS and realise "hey we're 
at operating temperature" and set the IAC to a "last known hot idle 
step count" instead of having to find the idle step count everytime I 
drive it.

I think a lot of this could be described as just slow IAC response to 
conditions.. and could probably even be corrected with minor mods 
to the idle lag filters.  (I have replaced the IAC with no effect, so it's 
not the IAC itself).  One day I hope to have enough knowledge to 
modify the BIN and tinker/fix it, but as of now I just don't have the 
technical knowhow to relate the assembly code (which i 
understand at face value, i have done assembly before on PC's and 
intel microcontrollers) to what it's actually doing to the ECM and 
hardware and external devices which control the engine.  My main 
problem is code recognition..it's extremely difficult (for me) to look 
at a bunch of ASM commands and figure out... "oh, this is a lag 
filter" or "oh, this is an idle control routine."  I can recognize simple 
stuff (like a table) but it's difficult to figure out just what the table is 
(spark advance or fuel curve or what).  I envy all you reverse-
engineering gurus!  And yes, I AM reading the 101's....

nick
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