Quadrajet gurus, help me out

[Slooptin]

I'm dialing in my truck (stock 454, no egr/emissions, quadrajet #17080812, ~36 degrees total timing w/ vac advance). mixture screws are about 2-1/2 turns from bottom and APT screw is about 3 turns from bottom. I'm running a vac gauge in the cab as well as an AEM afr gauge. For afr, I can get it to idle around 12.9-13.6 and running around 14.6-14.8 with acceleration around 15-16. I have 19-21 inHg at idle, but my idle is never steady, it jumps between 800-1100 and when i start the truck hot, it idles around 600 until I blip the throttle. sometimes it will idle smoothly (engine doesn't move at all) and sometimes its rough (engine shakes the truck). I'm just trying to get the truck to run consistently and it seems like I can get it set up to run smoothly and other times, it varies. any suggestions on why i cant get it to consistently idle smoothly?

 

[Snoots]

Very nice numbers!
Q-Jets tend to develop leaks at the throttle body where the actuators enter. Try squirting a little starting fluid on them to see if the idle changes.
Also, check the torque on the intake bolts.

 

[Matt69olds]

Try it with the vacuum advance disconnected. You may have the idle changing due to the advance coming and going.

If that solves it, you need a vaccum canister with a little more tension to delay advance.

 

[BlueMule]

Hey Sloop, there are a couple of things that can cause idle issues with Q jets

1. Debris in the idle wells, and possibly in the idle tubes. As the debris shifts you get a different idle air/fuel mix, and so the idle changes.

2. Air leaking at the throttle shafts

You might want to check for misc vacuum leaks in the engine as was mentioned by Snoots, but be careful with the starting fluid it's like suuuuuper flammable. Make sure your vacuum advance is not leaking, if you don't have a hand pump vacuum pump, you can use the old mouth as a vacuum pump method.

 

[fast 99]

Check that the centrifugal advance weight springs aren't loose, while in there turn the rotor make sure it snaps back, excessively loose primary throttle shaft [unless re-bushed they all slightly loose] throttle return spring and secondary throttle shaft not closing completely.

The under load O2 reading is a bit lean but shouldn't affect idle quality.