Recently my 89 Cutlass(with 2.8L MPFI) started putting out a Code 45.
Now my engine is doing something strange that it did back in early
March. In March it did it twice in one day, and then hadn't done it
again until today.
First, I drive to the store, am waiting in the car for my gf to come
out, and the SES light comes on. No big deal because I already know
that it's Code 45 and that I can literally see my A/F Gauge just
sitting in the RICH and not moving at all.
But then, I see my AutoMeter Vacuum Gauge is all bouncing around like
it did back in March and then I notice that my RPM/Idle is going
crazy, again, just like it did that one day in March.
Sometimes the idle would jump so low and almost stall that my digital
tach would go to zero, and then jump back up to 700...it would just
keep bouncing like that. At the same time my Vacuum was dropping from
like 17" hg to 5" hg and anywhere in-between. It too was all over the
I decided to check to see what would happen if I revved the engine,
and it revved perfectly. Then I realized that if I put my foot just
ever so lightly on the gas pedal, all the crazy stuff would stop
immediately, and smooth out!!?? As SOON as I took my foot off, it
would go crazy again. Now when I say "ever so lightly" I MEAN ever so
LIGHTLY! So barely was I on the gas pedal that I wasn't even putting
pressure on it...just the weight of my shoe would make the bouncing up
and down go completely away.
I sat idling like this for about 2 minutes...After my gf came out, I
put it in Drive, drove away, and it hasn't done that since! However, I
could see when I was at a Stop that sometimes the Vacuum gauge would
bounce very slightly by 1 or 2 hg, but not much more. I could kind of
tell the idle was a LITTLE bouncy because some of my interior lights
would brighten and dim ever so slightly, almost un-noticable.
So because this occurs so erratically, I haven't really been able to
fully diagnose what's going on. From what has happened I have the
obvious clues. For example:
For whatever reason, when I would barely touch the gas, and therefore
open the throttle just slightly, the erratic idle would immediately
stop. So this tells me that as soon as I let in a STEADY amount of
air, everything would smooth out. What I'm wondering is whether the
Code 45, a rich condition, is related to the erratic engine behavior?
I don't think it's the EGR valve because I've felt the idle of a stuck
open EGR and it wasn't like this.
As of right now, I would be it's in the IAC circuit. Another reason I
think it's the IAC is because shutting the engine off and re-starting
it will almost always cure the problem, and I know that when doing
this, the IAC Valve re-sets itself.
I was wondering what you all think??
PS If it is indeed the IAC Valve, could this also cause the Code 45
but not letting in enough(or the ECM's expected) air at idle?