I STILL can't figure this out...need the experts!

[gmrulz4u]

I recently posted about the Code 45 that I was getting. 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. But I was wondering what you all think??

 

THANKS AGAIN!

[Brian P]

Clean or heck, replace the IAC with a known good one, reset the computer and do a complete idle relearn. See what happens from there.

[sonyman87]

Brian P hit the nail on the head

 

IAC is probably not functioning correctly

 

i had that same problem and i litteratly tore the entire intake manifold off 3 times before i figured out all i had to do was turn the key to on position for 5 seconds and then off for 10 seconds so the IAC will relearn its open and closed positions

[Brian P]

the idle relearn Ive always done:

 

Remove and replace ECM fuse

start car without touching gas pedal- even if it takes forever to start

 

Immediately put in D and hold in gear with brake for 7 mins

 

shut off for 10 seconds

 

restart and repeat holding in D for another 3-4 mins, then take it for a quick drive.

[phantomshado]

where is the ecm fuse? :oops:

[topless94style]

where is the ecm fuse? :oops:

 

 

i believe its in one of the fuse boxes under the hood

[Brian P]

model years 1988-1993 it's next to the fuel pump relay and auxiliary positive terminal- remove the relay/fuse cover (bout a 2 inch square piece) and there ya go. May be there for later years too, haven't checked to be sure.

[gmrulz4u]

Thanks guys!

 

One other thing, isn't there a resistance test that I can do on the IAC Valves pins or something? I thought I could use my MultiMeter and check the ohms of the different pins etc...does anyone have the range that it should be?

[95DropTop]

When I was test driving the convertible for the weekend, I had the same problem, although it happened more than once during the weekend. Turns out there was a leaking vaccuum hose on the passenger side of the engine. Little plastic piece had cracked and I could literally hear the hissing. Got that fixed and thought it was cured, but it turns out there was also a lower intake leak...mech sprayed some starting fluid? around the gasket area and if the idle changes, you have a leak. Also, the only other symptom was at first start up, the idle went up to about 3k then slowly came down. The trans would shift hard into gear during the first few minutes after startup. After a few miles, it heated up and sealed the leak and it got much better.