1999 mit mirage idles fine in park and reverse, but rough and sometimes stalls in forward gears . changed plugs ,wires,cap and air filter

You need to check your Idle Air Control (IAC) that is located on the throttle. When you change your transmission to a forward gear that gives the computer a signal and then the computer gives the IAC the signal in order for it to control the idle as needed, but if the IAC is damaged it wont work properly. I have had this problem in several cars in my shop and the cost of a rebuild IAC with the throttle is about $300, so good luck.

U may need to have ur idlein ajusted to specs