On my '89 I have been having problems with "hanging RPMs" so I bought the restrictor gasket sold on Ebay ($6.00, shipping free). The gasket is quality so it is a good buy. Before installing it, I took of my TB and gave it a thorough clean. It wasn't too bad to begin with. As i mentioned in another post, I replaced the TPS as well because I thought it was a problem. While all was off, I found out that I had a IAC gasket attached but the holes were bigger than the new one. Though I installed everything back including the new gasket and it sounds better during shifting, but here are my concerns....if applicable.
The new gasket came with two holes for the TB ports, 11/32" and 9/32". The directions in essence says to "play" with both holes and pick the best. But if you have a a 5.0, suggestion is to increase the 9/32 hole to 11/32. Also, if the air doesn't work with the holes of the size given, chip away a little at a time to increase the holes to get it right. Now I didn't go through all of that. My first question is this, does the IAC ports have different duties? What I mean is that if I try the gasket one way and then flip it to use the different size hole, should there be a differnce in idle? I ask because I tried the gasket both ways, but didn't notice a difference in the idle. I disconnected the positive cable becasue I see it connected to a solenoid and other things (assuming computer connection) and I wanted the truck to re-learn. The problem is that the truck continued to run with the postive cable off. I then removed the negative and the truck contined to run. That is, BOTH cables were disconnected and the truck was still running, is that normal or is there something else wrong that I need to look into? The hood light went off after the negative disconnection but as I mention, the truck still ran. Now, finally, the idle did drop when I cut the truck on and stay idled, but it still hangs a little. Should I open the holes up more or leave it as it is? Hope you can follow me.

 

You just need to disconnect the negative cable (with the truck off) for the computer to reset. It's good practice to never disconnect the positive first.

The larger you make the holes in the restrictor, the less effect it will have.

 

that can be one of the worst things your can do, you can fry your computer! Don't ever take the ground off while the vehicle is running. (you could do this back in the 50's-60's when cars had generators instead of alternators) but the point is, theres nowhere for the excess current from the alternator to go when the vehicle has no ground so it can send voltage spikes throughout your wiring and fry those 5v sensors as well as your computer.

 

the truck kept running cause you were just running off the amps the alternator were pumping out.... a car will run without a alt (till the battery dies) car will run without a battery (battery needs to be in place to start though) but afterwards the battery can be taken out as long as the poss cable dosen't tough metal. Like the others said, not always a wise practice, B U T if needed to do so, always hook up the poss first, then the neg. the no neg cable check is a sure way to tell if the alt is getting juice out to the battery or not, if not the vehicle will die after the neg is removed.

 

O.k., I got the battery cable "no-no", and thanks for the information. Now about the restrictor. There are two ports, do they hold different responsibiliites, i.e, exhaust, intake? Should I turn the gasket to one or the other??

 

I might be totally wrong, but I think that one hole draws air into the IAC before the throttle butterflies, and the other hole lets it in after the butterflies. Basically lets additional air in without the throttle being open on cold start.

If that's correct, I don't see what difference the placement would make. The smallest hole should be the actual 'restriction' no matter which side it's on.

If my understanding is wrong, there might be more to it...

 

Cool, like I said, I really didn't notice much difference in the idle itself if I push on the pedal. Before, cold it would idle high, then I would have to depress /release the pedal then it would lower idle. But now at start up, it idles low but enough to keep sound (I didin't look at the RPMs). Also the rpms drop great to allow shifting without the hang-up in RPMs and it is alright. It doesn't have a great take off now, it is a little slow to catch up. But if it doesn't matter which way, I will leave it alone for a while. I haven't taken it on any lengthy ride just yet, but I have a camping trip that will take about two hours of driving. We will see then.