88 Deville stalls constantly.

Well, I thought it was the fuel filter but problem persisted. It stalls when I let off the gas pedal, to cost or stop etc. The service soon light pops on for a split second then it'll stall. Takes several attempts to start the car back up.
I found I can keep it from stalling if I keep the accelerator pressed down with out ever letting completely off of it. Even at stop lights (with brake applied of course.)
I'm thanking of changing the EGR valve. If someone could please let me know if maybe the problem could be else it could be. I've seen other suggestion like the crankshaft position sensor. Any and all help is very much appreciated.
Thank you.