CVO 6/29/2012The fuel filter is last for 20K miles. First, try the fuel filter and if it won't help.
Check the FUEL SYSTEM PRESSURE
1998 Buick Riviera 3.8L SFI SC OHV 6cyl
The Fuel System Pressure
48-55 PSI (Pounds per Square Inch)Position the ignition switch and the A/C system in theoff position. Install a fuel pressure gauge to thevehicles fuel rail or fuel pressure test port.Confirm that no leaks are present, and visuallyverify the PSI reading on the gauge with the ignitionin the on position.
Note : replace the fuel pump if it isn't in the specifications.
alvin 7/8/2012This is a problem thats probably related to the crank senor.