My 1999 Volkswagon Passat wagon 1.8 liter has been

My 1999 Volkswagon Passat wagon 1.8 liter has been having random bogging problems usually off the line. The ignition module was replaced a year ago along with a tune-up. The engine light is currently not coming on. Was told since there is no light, the module should be fine and to maybe replace the fuel filter. I have also checked the spark plugs..which were fine. What do you think?