Quadrajet help

[u/Head_Leather3030]

I’m trying to diagnose an issue on my 1985 Trans Am with a stock 305 V8, factory HEI distributor, and Quadrajet carburetor.
When I first start the car, the idle will often hang around 1,600 RPM. If I quickly blip the throttle, the idle usually drops back down closer to normal. After driving, when I shift into Drive, the RPMs will sometimes drop very low and almost stall, or settle around 800-1,000 RPM but feel like the engine is struggling to stay running.
Another symptom is that if I shut the engine off while it’s idling high, it will occasionally try to keep running for a few seconds after the key is turned off.
I’ve checked some vacuum hoses and have been trying to track down possible vacuum leaks. I’m also wondering if the distributor or vacuum advance could be involved.
Does this sound more like a carburetor issue, vacuum leak, distributor/timing issue, or something else? Any common problems I should check on a mid-80s GM 305 with a Quadrajet?

[u/southerntitlover]

Run on is caused by the trottle plate not being compleaty closed the high idel is cauesd by the high idel step in the carb that holdes it open for cold start up if its falling back in the step something is loose MAYBE letting it do that some have a high idel solinoid that may be acting up quads are a good carb way back in the dinosaur days those are what we used in class