I recently changed the spark plugs and wires, distributor cap, fuel filter, and checked the main relay. Its a 91 ls. Sometimes the car starts up and runs strong like nothings wrong, but others it will crank but not start and i have to wait awhile and keep trying. Every once in a while it almost starts but bogs down and i step on the gas and white smoke comes out of the intake filter and it dies. But then after that it will eventually start and run good again.

Also, sometimes when i am driving it will drop in rpms and jump back up, or completly shut off then turn back on a minute later as i coast.

Any suggestions on what could cause it to do this?