background : 85 FB 2.8, T5

I have done a lot of searching on this issue and read the tech article but still am a bit confused as there are varying answers throughout the threads. Questions.

1. someone stated that the ECM can only add air and not take away, thus minimun air has to be less than target idle....makes sense. I was examining things last night and the throttle lever is completely against the idle screw at idle (approx 850 - 900rpm). I am assuming by the previous statement that I should have a gap there at idle???

2. Haven't touched min air yet but have heard varying opinions on the rpm (400, 450, 600, 650). I don't have the GM manual yet (only haynes which has nothing about these ajustments) but is there a stated value in the manual? It said 450 in the article but I wasn't sure if that was for the V8 or both or what? Did that # come from the manual?? What would the effect be it it wasn't at that value??

3. All this talk about grounding the ALDL terminal (and starting the engine) and frying the ECM is making me nervous. What is the purpose of grounding it, to reset the IAC?? So the computer doesn't control the idle? What would be the effect if you unplugged the A - B jumper before starting?

4. and lastly, I am assuming the the big bold underlined letters on my VECI label saying "DO NOT ATTEMPT ADJUSTMENTS" refers to trying to adjust the idle via the idle screw only (I assume this is on everyone's label?)?? and that adjusting min air does nothing to the idle rpm (ECM controlled, right?)??

any help / comments to help me better understand this (and prevent damage) would be greatly appreciated.

thanks.

thanks

 

isn't there anyone that can help me out here???? I am still confused about these issues.

 

i used the idle screw thing located on my Throttle Boddy to adjust my idle. (it was a little low and stalling when i stopped at stop signs, etc)

So, it is possible to adjust idle via the screw.

 

i thought yopuweren't supposed to do that though unless you have the IAC disconnected because the ECM controls idle??

 

well my ECM was doing a **** poor job, so i left the duty up to the good ole, very reliable SCREW!

 

Well, I might not be much help here, but...

1) ECM should be able to extend/retract the pintle of the IAC motor as necessary to allow more air in or keep air out. Correct, the throttle lever should be against the idle screw.

2) Don't know about that; in 251,000 miles (note: original engine!), I've never had to adjust my idle.

3) I've never started the car with the jumper in the ALDL, either. (See number two!)

4) That's just to keep general morons who don't know how cars work from messing with the idle! There's actually an aluminum plug covering the idle screw that you'd have to remove with a punch in order to get at the head of the screw; GM sealed it from the factory.

Any reason why you want to change the idle?

 

thanks TomP, you are a help (in many ways, after seeing many of your other threads )!

Ok so the lever does go right against the screw...wasn't sure on that one because the cap you speak of has already been removed by a previous owner so I figured maybe someone just cranked that up to fix things.

I wasn't necessarily going to change the idle, more of a checkup to see if the min air is right etc due to idel and stall problems (as mentioned, who knows what the previous owner did?). I have to get rid of a minor leak at the PCV valve first and then see how the idle is....don't laugh, I've currently got a spark plug elbow on there because the other one broke off and GM wants almost 20 bucks for just the grommet! The combined vacuum line set up that includes the PCV also has to be replaced but I have to do a "homemade" fix because all the ones I have found don't have the extra branch to the decel valve found with T5's (GM discontinued).

But anyway, the symptoms are stalling (somtimes) when stopping and a varying idle, so I just thought I'd check everything at once. I will definitely clean the IAC as per your other post.

Just out of curiosity, what is the spec for our idle (again, I have a T5). Currently it is approx 900.....is this about rightor should it be lower???

I figured something like that....but I guess I am one of them just for asking