ENGINE IDLES ROUGH, BUT RUNS FINE WHILE DRIVING. My car is a 1995 Buick Regal Gran Sport with the 3800 series motor with 212000 miles. The rough idle tarted after driving through some muddy and wet roads

Go the cheapest route. replace fuel filter and add SEAFOAM to tank of premiun fuel. replace filter before 500 miles. then add SEAFOAM to gas every 3000 miles to keep lines.engine,fuel pump, and emissions systems clean, ETHANOL problem number 3000

Check all vacuum lines for leaks. Check spark plug wires for and spark plugs that may be worn and causing idle misfire.