ford escort starting problem

I HAVE A 1993 FORD ESCORT LX .THE PROBLEM IS THAT WHEN YOU START THE CAR YOU HAVE TO PUT IT IN DRIVE OR REVERSE OR IT WILL CUT OFF.THIS WORKS WHEN THE CAR IS COLD BUT AFTER IT WARMS UP YOU HAVE TO TO IT A COUPLE OF TIMES BEFORE IT WILL REMAIN RUNNING.SOMETIMES IT WILL RUN IN PARK BUT IT KEEPS IDLEING UP AND DOWN,MOST OF THE TIME IT JUST CUTS OFF.WOULD APPRECIATE ANY HELP!!!!