we need to know what is the fuel pressure where it is going into the ip (injection pump). Best is to put a metal T fitting AFTER the last rubber hose because the fuel line deteriorates from the inside out so while it looks and feels normal the inside is causing problems. Sounds crazy but seen it dozens and dozens of times.
TOO MUCH PRESSURE IS BAD. 8psi max but it will advance timing at that level. It should be 5psi if the ip is stock (not hot rod built).
Take pictures of the ip. I need to see what is happening: my own nephew has the throttle cable retainer clip gone and his cable will bind on occasion.
Also close up pic of the cable itself where it comes out of the cable liner at the ip and at the pedal. Ive seen cables gummed up and others that one strand comes free and can bind it. Disconnecting it from ip linkage and operate pedal and cable alone- it should be smooth as glass.
Make sure the high idle solenoid is not creating a problem- again pics and we can see if it is.
You have some super knowledgeable individuals here happy to help, so it’s worth the time for pics, or videos onto YouTube, bitchute, etc and post link.
This is a rare one to cause high idle- but I have seen one time where air intrusion was the culprit.
Replace your 1/4” diameter 5” long ip fuel return line with clear tubing.
Sold by the foot at hardware stores and it will last about 3-5 years. Or buy the good stuff from fuel-line.com and it is good for many years.
The clear line is the FIRST thing on the Standyne & GM diagnostic list. Simply start engine & watch for traveling bubbles, contaminants, etc.
