Engin speed varies on 1992 Ford Taurus

My engine speed goes up and down in park after car is warmed up. Put it in drive it sometime dies

Asked by for the 1992 Ford Taurus
My wife and I have a 2.5 that had the same problem. For us, we had to replace the IAC valve (Idle Air Control Valve). It ran with very low idle, and nearly stalled when put in drive. It cost us $50 to $60 and replacing required two bolts and unhooking the wires.First, have the codes read, then go from there.If you have a returnless fuel system, have the fuel pressure sensor checked out.