Ok, it seems to me that my car (92 Camaro, 3.1 MPFI) idles a little high, and it fluctuates a little bit once it warms up.

Nothing serious, the car runs great, but I'm still going through the motions...

My brother has an 85 Firebird, 2.8 MPFI that we've been tinkering with for some time. We decide we might as well do them both at the same time.

I just cleaned my IAC valve (and he cleaned his) then we go to adjust our minimum air... Small problem, my car does not specify what RPM it is supposed to idle at (because it doesn't want you adjusting it) and his has a formula hood on it, so it obviously doesn't either (and if it did it would be wrong).

Anybody know the specs for both of these motors? I tried searching, came up with nothing.

Now... Another question about this... On the page I found that walks you through it, it tells you to jump your ALDL, turn your ignition on, wait 30 seconds, unplug your IAC, then "start your engine".

It doesn't specify if I unplug the ALDL before I start the motor, and it goes against my better judgement to start it up while the diagnostic terminal is grounded out. The last thing I need is to replace an ECM on my perfectly running car... Is it ok to do this?

 

Idle Adjustment Procedures are in this thread:
https://www.thirdgen.org/techbb2/sho...hreadid=235452

The procedures for the 2.8L and 3.1L engines are listed.
When the 3.1L procedure talks about monitoring the IAC valve counts, that involves using an ALDL scanner or a laptop with ALDL cable and software to monitor that number.

 

Would I HAVE to use a diagnostic scanner just because I have a 3.1?

If I go about setting mine the same way I set his, it should still set me up for a better baseline and would do no harm, correct?

 

you don't have to have any aldl software hooked up to reset the IAC...just to monitor it.

 

Ok, I already cleaned the IAC and put it back in (making sure it wasn't over-extended), now I'm going to set the idle.

I don't see what the talk of scanners and laptops was for, I'm just setting my idle here buddy.

Just wanted to make sure of the ALDL thing and find where it should idle at. (I notice I suck at finding stuff with the search)

 

Damn...

I guess I can't do it like that.

When I unplug the IAC after it's been sitting in diagnostic mode for 30 seconds it will no longer start.

Wierd...

 

Huh? What exactly do you mean by reset the IAC?

I don't have a 3.1L car, so I've never tried the procedure in that thread.

So you are trying to use the 2.8L procedure on your 3.1L? Or are you having problems with the 85 Firebird 2.8L you mentioned?

 

Ok, you jump the ALDL and turn the key to on, this puts the IAC motor to what's called "0 counts." This means that it is 100% fully seated and closed. You then turn the ignition off and unplug the IAC motor. This forces it to stay fully closed. You can leave the ALDL grounded, or not, doesn't matter, but then you set the idle speed to whatever is specified, I think it's something like 450 or 500 rpm or something, just at the point where it'll run by itself. Then you turn the car off, plug the IAC motor back in, and life is good. It'll idle right around 750 to 800 rpm if everthing is right.

 

Um, that's essentially what the procedure linked to above instructs you to do, it's just in a step-by-step form.

Also, the Chilton's manual that I took that step-by-step list from and elaborated on listed a different procedure for the 3.1L engine (which is show in the thread above). I don't know why the 2.8L and 3.1L are supposed to be adjusted differently...

 

i believe that they actually use a different IAC...that would be why they have to be set/reset differently.

 

The 2.8L and 3.1L engines also use different computers/ECMs (as I'm sure you know).

 

When I unplugged the IAC on my 3.1 the car would no longer run.

The 2.8 adjustment went fine.

Our IAC's housing was slightly different, but the connector and the valve itself looked to be exactly the same, the only difference being my housing was setup to use an O-ring for sealing and his was a flat surface requiring a gasket.