‘74 1.8L L-Jetronic idle hang… SOLVED!, Thanks everyone! Options

[Van B]

Evening everyone. So, I installed the proper intake boot from auto Atlanta this afternoon but the car still isn’t behaving properly.
Basically, when the car is warm and I go from driving at speed to a stop, the rpm hangs around 1600-1800. Once stopped, I can sometimes blip the throttle and get it to fall to around 1100rpm. If I load the engine by partially releasing the clutch, I can get the car to idle normally at 800-ish and it stays there.
Also, there is no hunting, surging, or problems with idling over a long term.
I just can’t understand why it hangs when I’m out driving.

I’ll run through the things I’ve checked so far and hopefully someone with more experience can help.

First I took off the Aux Air Regulator and confirmed it is functional.

Replaced the boot and discovered the one installed was not correct for a 74 1.8L
- that meant I had to replace and sort out some vacuum lines that were not correct length and get a substitute for the small fitting on the boot.

Put clamps on connections that didn’t seem tight enough.

Had the car smoke tested when I bought it and the mechanic said the boot was the only thing leaking.

Could the barn door on the AFM be hanging up or too loose?

Thanks!

Van