Hello. I have a 1970 Ford Econoline e100 V8 302 engine with manual transmission. I recently had a new fuel pump, nee spark plugs, new fuel filter and carb cleaning done. The engine is very strong and runs well. The only oddity is that sometimes when I pull up to a light it idles slow, and other times it idles fast. Can you tell me what the most likely culprits might be and how to fix? Thank you

 

Most likely you have a vacuum leak---temporarily install a vacuum gauge inside the cabin to monitor that reading as the idle speed changes. If it fluctuates consistent with idle speed then start looking for a leaking hose, perhaps one rotted due age?