Ford Repair: erratic idle, oxygen sensor, rough condition

Question
1995 escort wagon 1.9l standard trans. Idle is erratic, engine will maintain idle speed for approx. 1 min. when at oper.temp. then will suddenly drop 300/400 rpm with a rough condition. opening the throttle will stop the problem temporaly, but will repeat the same cycle. plugs are clean, wires test ok, p.c.v. ok, replaced Oxygen sensor, no notable difference.

Answer
Hello and thanks for the question...I'll try to help.
 What I would suggest is that you bring it to a garage and have the computer checked for fault codes. Before that, IF your vehicle has a EGR valve (so do, some don't), check to see if it is stuck open or closed.
Hope this helps,
Erik