1992 Ford E-Series Van Hugh idle

Check for dirty and or binding throttle or linkage, and vacuum leaks. Get a can of spray gumout, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!
To clean the throttle and bore, use only a mild cleaner, Ford treats these with teflon, harsh cleaners will destroy this coating.