[This message has been edited by A_Lonely_Potato (edited 10-06-2022).]

quote Originally posted by A_Lonely_Potato: there seems to be a lot of air gap around the throttle plate...

Bingo!

In my experience, the throttle plate should be only be held open enough at idle by the stop screw to prevent the plate/valve from binding in the TB bore.* I suspect that what I earlier suggested has indeed occurred! Never underestimate what a previous owner/mechanic may've done.

quote Originally posted by Patrick: I suppose it is possible that someone could've reinstalled a plug after changing the idle stop setting, but that doesn't seem too likely.

* There is a "proper" procedure for returning the idle stop screw back to the factory setting. If you have trouble locating it, I can probably find it.

[EDIT] Is the end of the throttle stop screw actually what is preventing the throttle from closing any further? In other words... Is there any chance that the two screws holding the throttle plate in the shaft have been loosened/removed and the plate re-positioned somewhat, just enough to possibly prevent the plate/valve from closing all the way? Doubtful, but I'm trying to imagine any/all potential scenarios.

[EDIT 2]
Looking at this closer, it actually does look like the throttle plate may have been shifted on the shaft.

[This message has been edited by Patrick (edited 10-06-2022).]

quote Originally posted by Patrick: * There is a "proper" procedure for returning the idle stop screw back to the factory setting. If you have trouble locating it, I can probably find it. [EDIT] Is the end of the throttle stop screw actually what is preventing the throttle from closing any further? In other words... Is there any chance that the two screws holding the throttle plate in the shaft have been loosened/removed and the plate re-positioned somewhat, just enough to possibly prevent the plate/valve from closing all the way? Doubtful, but I'm trying to imagine any/all potential scenarios.

I actually took the plate out after seeing the gap, and cleaned it and the TB bore up some. I fiddled around with different rotations for the plate install, but none of them kept it really seated. The screw is definitely what is stopping it. You cant see it in the image but there was air gap around 100% of the plate, although miniscule at the sides, it was still clearance, so the plate couldn't be stopping it.

I'm pretty sure i've read through the procedure somewhere on here, i'm sure i can find it with search.

quote Originally posted by Patrick: Never underestimate what a previous owner/mechanic may've done.

It just seems so bizarre to cover that back over, let alone to adjust it in the first place. Mention doing that on this forum and you'll have people show up at your doorstep in 3 minutes haha.
EDIT: Found this, tomorrow when its dry out i'll give it a go. Got rained out today :/

quote For the ECM to properly control idle, the throttle stop screw must be set for "minimum air". This is a process that sets the idle with the IAC fully extended. To fully extend the IAC, jumper ALDL pins A and B together (just like when you check codes) and turn the key on, but do not start the car. With the key on, not running, and in diags mode, the ECM will keep trying to fully extend the IAC. After 30 seconds or so, pull the IAC connector off the IAC *before* doing anything else. This will capture the IAC fully extended. Now pull out the jumper in the ALDL, and start the car. Typically the "minimum air" idle speed is in the 500 RPM range. I find the car can bearly run at 550. So as long as you can get it to idle on its own between 600 & 700 your good. Set the idle using the throttle stop screw. (The engine should be fully warm to do this.) Now shut the engine off and reconnect the IAC wires. The ECM does not know where the IAC present position is, so pull the ECM fuse (or disconnect the battery) for 20-30 seconds. (This will cause a complete ECM reset of all learned parameters, including the learned IAC ones. Then reinstall the ECM fuse. Turn the key on, wait 10 seconds or so, and turn the key back off. This will now reset the IAC to a known key-off "park" position. Now start the car. The engine should idle properly under control of the ECM. There are some learned values, such as an IAC offset for A/C, etc that need to be learned, but this will happen under normal driving conditions. I suggest driving the car right away under all conditions. Stop & go, steady cruising over 45 mph, full throttle, and so on. Pull over a few times and turn the car off, then restart it. The IAC can only learn X amount of counts with each run position. If everything else on the engine is in good condition and operating properly it should be around 900 RPM after coming to a complete stop with slight variations and improve over time.

[This message has been edited by A_Lonely_Potato (edited 10-06-2022).]

quote Originally posted by A_Lonely_Potato: I actually took the plate out after seeing the gap, and cleaned it and the TB bore up some. I fiddled around with different rotations for the plate install...

Ah... okay, that explains what I saw in your photo! You may be able to better center the plate on the shaft when you temporarily back the idle stop screw right out so that the throttle closes all the way (...and then re-set the idle stop).

[This message has been edited by Patrick (edited 10-06-2022).]

quote Originally posted by A_Lonely_Potato: The gap was like that before i took the plate out.

Oh, I don't doubt it... but I was more referring to the plate now being a bit offset in the shaft.

quote Originally posted by Patrick: Ah... okay, that explains what I saw in your photo! You may be able to better center the plate on the shaft when you temporarily back the idle stop screw right out so that the throttle closes all the way (...and then re-set the idle stop).

If you look closely at the enlarged photo that I posted above, you can clearly see that the plate has been re-positioned to the right. Not only is there evidence of the original shaft position marked on the plate (indicated by the arrows), but notice the difference in light getting past the plate on either side. Way more light to the left of the plate.

[This message has been edited by Patrick (edited 10-06-2022).]