An engine vacuum leak may develop from the throttle body gasket causing a higher than normal idle speed. Failed gaskets should be replaced.
Car Problem Reports
GMC Vandura 2500 Idling Problems Due to Vacuum Leak in Throttle Body Gasket
GMC Vandura 2500 Problem
Engines Affected: 5.7L V8, Gasoline
Visitor, 1995 GMC Vandura 2500, 5.7L V8, 169,000 mi
the van began minor irregular jerking while traveling at highway speeds as if ignition were missing in an irregular pattern. We then noticed that the engine seemed to be idling fast. Mechanic replaced the throttle barrel gasket which corrected the fast idle and the jerking seemed to be cured also,but on the first trip of some distance, the jerk began at about 30 miles out and continued to randomly occur for the 400 mile trip