random idle issues

[91MMY59]

1989 MM with a 2.0l carb'd engine. 130k 1 owner miles. truck starts right up,runs great has plenty of power...except about once every 3 weeks I will get high idle when I start and drive. after about 2 days,it goes back to normal.
it will pull itself about 40mph on the hiway with no gas applied when it decides it is haunted.:))
any ideas to look for will be appreciated.thanks

[Law Dog]

Check and see if the throttle is not sticking maybe add a better return spring to it! Seen that happen a lot on the stock and my Weber both.

[ragragtimetime]

check for worn linkage, smooth throttle operation, worn/loose vacuum hose connections (issues change/occur @ various times as engine warms), check choke for fully open & fully closed positions (may stick causing other linkage to not operate), sub egr also will cause linkage movement issue (& is very easy to clean...just don't drop any of those tiny pieces). i use gumout spray "carb + choke cleaner" (& would not hesitate on using most of the can) as it will clean & not leave oil residue that may accumulate dirt & cause it to be cleaned again (i have a long gravel driveway). i you feel the need for lubricant i recommend a "dry graphite lube spray" instead of petroleum base. absolutely try the inexpensive fixes first then throw your wallet at it. best of luck!