Code 45 and a CRAZY idle...

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 place.
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??
THANKS AGAIN!:)
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?
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IAC circuit sounds reasonable. Many times just removing it and cleaning it helps a lot. Also, don't forget that your oxygen sensor is the sensor detecting the rich mixture. So suspect the oxygen sensor as well. Of course this is all coming from me, who doesn't know your car as well as you do. But I would suspect the oxygen sensor more than the IAC circuit. A map sensor is also perfectly capable of creating a rich condition, but more likely than not your ECM would detect a voltage out of range. Your idle could be the result of a vacuum problems, or vacuum problems a result of too low of an idle. Which the second sounds more reasonable to me.
Tony
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My first thoughts would be a ditry throttle body. These puppys get pretty dirty, especially over 100K miles. Since they do not have fuel flowing thru them, most people never think to clean them.
Some times a can of gumout carb cleaner will fix the problem, more often you need to remove the throttle body and clean it with a tooth brush and carb cleaner. I use gumout which is sensor safe. A typical cleaning will use a 1/2 can or so. You should also clean the vaccume ports in the top of the throttle body, as well as the springs on it, and around the throttle shaft.
Labor wise, it's about an hour job, cost wise less then $25 unless you break the plastic vacume lines. Charles
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Is code 13 also stored with the code 45?
Code 45 is set when the Oxygen sensor stays at a Rich condition for more than 45sec. Once that occurs; the ECM turns on the SES>turns Off the canister purge solenoid, air management solenoids and switches to Open Loop operation.
It can also be caused by Ox sensor circuit faults(electrical) or the air-fuel ratio rich due to a fuel control or emisssions system fault.
Dave S(Texas)
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