Slight voltage changes = unstable idle?? ECM EXPERTS!!!

I own a 1989 Cutlass Supreme(2.8L MPFI) that I cannot for the life of
me seem to figure out.

It's doing a LOT of strange things, that to me, are indicating a
faulty ECM.

First off, I've noticed that once the engine is up to operating
temperature(200 degrees F'), it starts to get "sluggish" and the idle
starts to act-up. I recently noticed something even stranger in that
for some reason, VERY small, and I mean like 0.2-0.5 volts, voltage
drops are affecting the engine. For example, if I turn my four-way
flashers ON, and the four-ways flash ON and OFF...I can literally sit
there with the engine running, and watch, hear & feel the engine kind
of "stumble" a little when the lights go ON, and quickly smoothen-out
when they go OFF...so as the four-ways are flashing ON and OFF, each
time they go ON, there's a little hesitation in idle...then they go
OFF, and it's smooth...it will just keep doing this until I shut them
off.

My two biggest helpers in figuring out what's wrong is my AutoMeter
Vacuum Gauge and my AutoMeter A/F Gauge(O2 Sensor). Going back to the
above, every time the four-ways flash ON, I can see the engine's
vacuum drop almost 2" hg to about 15" hg. When they flash OFF, it
goes back up to about 17" hg. So as the lights are flashing, I can
sit and watch the engine vacuum continue to flucuate up and down like
this until I turn them off. So I KNOW that something really is
happening and that I'm not just "hearing" things.

Now I should let you know that's it's not just the four-ways...it's
ANY electrical load...even just opening the door which results in the
interior lights turning on causes the exact same thing...I can also
watch the battery voltage while this is happening with my digital
multi-meter and the voltage isn't even dropping half-a-volt during
these times!!?? It's always steady around 14.4 volts and might drop
to 14.1 when the four-ways flash...

I've already made sure that it's not the battery or alternator causing
any of this. Both are not even 1 year old and working perfectly.

Now, moving on...

For the past few weeks I've been getting a frequent code 45, meaning a
Rich exhaust. My O2 Sensor is almost 2 years old. I've also got a
code 44, Lean exhaust, once or twice. BUT!, here's the strange thing:
A code 45 is only supposed to set when the throttle is between 3 and
45 percent, but my engine is ONLY running Rich at idle, when I'm at 0%
throttle. Again, thanks to my AutoMeter A/F Gauge, I can see that 75%
of the time I come to a complete STOP, my O2 Sensor sticks RICH and
doesn't move...until I start to drive again.

Today, I was idling in Park...watching my A/F Gauge...it was going
back and forth nicely...and then SUDDENLY, the SES Light came on, and
the O2 stuck rich again!? All this happened in a split second...which
again doesn't make sense because code 45 shouldn't be set unless the
O2 is sitting Rich for 50 seconds, not 1!!

And again, the SES Light for code 45 has ONLY ever come on while I'm
idling...even though it's not supposed to unless I am between the 3
and 45 percent throttle angle!!?

Last but not least...a few times in the past couple of weeks the idle
will all-of-a-sudden go crazy! Three times, the car wouldn't start
unless I opened the throttle(closed IAC)...if I could get it to BARELY
run, I would pull over, shut if off, re-start it, and then everything
would be fine!!?? It's almost as if the ECM is losing control of the
IAC or is losing it's IAC memory and can't remember what to do with
it...

So, to sum everything up:

1) Engine is "stumbling" slightly when voltage dips a half volt or
less

2) ECM is setting codes even though criteria for code is NOT being met

3) ECM is losing control of IAC or "forgetting" IAC positioning

I'm guessing it's time to get a NEW ECM??

The only thing that's stopping me from doing so is the O2 Sensor. I
know that the O2 Sensor is independant, and not "controlled" by the
ECM...so why will the O2 Sensor sometimes just suddenly STOP above 0.7
volts(RICH) and not move!!??

Help is greatly appreciated!!! Sorry for being so long...

The first thing to do is check all the system grounds for corrosion. The O2
sensor sticks rich because there is too much fuel in it....


"good4u" <mrbrnz@yahoo.com> wrote in message
news:c38e7694.0406151615.33297bb@posting.google.co m...
> I own a 1989 Cutlass Supreme(2.8L MPFI) that I cannot for the life of
> me seem to figure out.
>
> It's doing a LOT of strange things, that to me, are indicating a
> faulty ECM.
>
> First off, I've noticed that once the engine is up to operating
> temperature(200 degrees F'), it starts to get "sluggish" and the idle
> starts to act-up. I recently noticed something even stranger in that
> for some reason, VERY small, and I mean like 0.2-0.5 volts, voltage
> drops are affecting the engine. For example, if I turn my four-way
> flashers ON, and the four-ways flash ON and OFF...I can literally sit
> there with the engine running, and watch, hear & feel the engine kind
> of "stumble" a little when the lights go ON, and quickly smoothen-out
> when they go OFF...so as the four-ways are flashing ON and OFF, each
> time they go ON, there's a little hesitation in idle...then they go
> OFF, and it's smooth...it will just keep doing this until I shut them
> off.
>
> My two biggest helpers in figuring out what's wrong is my AutoMeter
> Vacuum Gauge and my AutoMeter A/F Gauge(O2 Sensor). Going back to the
> above, every time the four-ways flash ON, I can see the engine's
> vacuum drop almost 2" hg to about 15" hg. When they flash OFF, it
> goes back up to about 17" hg. So as the lights are flashing, I can
> sit and watch the engine vacuum continue to flucuate up and down like
> this until I turn them off. So I KNOW that something really is
> happening and that I'm not just "hearing" things.
>
> Now I should let you know that's it's not just the four-ways...it's
> ANY electrical load...even just opening the door which results in the
> interior lights turning on causes the exact same thing...I can also
> watch the battery voltage while this is happening with my digital
> multi-meter and the voltage isn't even dropping half-a-volt during
> these times!!?? It's always steady around 14.4 volts and might drop
> to 14.1 when the four-ways flash...
>
> I've already made sure that it's not the battery or alternator causing
> any of this. Both are not even 1 year old and working perfectly.
>
> Now, moving on...
>
> For the past few weeks I've been getting a frequent code 45, meaning a
> Rich exhaust. My O2 Sensor is almost 2 years old. I've also got a
> code 44, Lean exhaust, once or twice. BUT!, here's the strange thing:
> A code 45 is only supposed to set when the throttle is between 3 and
> 45 percent, but my engine is ONLY running Rich at idle, when I'm at 0%
> throttle. Again, thanks to my AutoMeter A/F Gauge, I can see that 75%
> of the time I come to a complete STOP, my O2 Sensor sticks RICH and
> doesn't move...until I start to drive again.
>
> Today, I was idling in Park...watching my A/F Gauge...it was going
> back and forth nicely...and then SUDDENLY, the SES Light came on, and
> the O2 stuck rich again!? All this happened in a split second...which
> again doesn't make sense because code 45 shouldn't be set unless the
> O2 is sitting Rich for 50 seconds, not 1!!
>
> And again, the SES Light for code 45 has ONLY ever come on while I'm
> idling...even though it's not supposed to unless I am between the 3
> and 45 percent throttle angle!!?
>
> Last but not least...a few times in the past couple of weeks the idle
> will all-of-a-sudden go crazy! Three times, the car wouldn't start
> unless I opened the throttle(closed IAC)...if I could get it to BARELY
> run, I would pull over, shut if off, re-start it, and then everything
> would be fine!!?? It's almost as if the ECM is losing control of the
> IAC or is losing it's IAC memory and can't remember what to do with
> it...
>
> So, to sum everything up:
>
> 1) Engine is "stumbling" slightly when voltage dips a half volt or
> less
>
> 2) ECM is setting codes even though criteria for code is NOT being met
>
> 3) ECM is losing control of IAC or "forgetting" IAC positioning
>
> I'm guessing it's time to get a NEW ECM??
>
> The only thing that's stopping me from doing so is the O2 Sensor. I
> know that the O2 Sensor is independant, and not "controlled" by the
> ECM...so why will the O2 Sensor sometimes just suddenly STOP above 0.7
> volts(RICH) and not move!!??
>
> Help is greatly appreciated!!! Sorry for being so long...