92 B2600i 4x4 Fuel Pressure Regulator/Idle
 

I've had an idle problem with my truck for years having spent hundreds of dollars at mechanics shops trying to get it fixed, to no avail. Got the ECU fixed,that's not it. A mechanic said it's probably the Fuel Pressure Regulator,which was new to me. Any thoughts on whether that affects idle at all? Can it be fixed or do I need to replace it? Help!