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Maybe someone can help me. I have a 99GT with no engine mods no offroad pipes, only flows and 4:10s. I had a serious idle problem this last week and Saturday I spent the day changing all O2 sensors and IAC motor, all plugs and checking voltage on all sensors I could reach. Everything checked out. After this , the car would not idle at all for more than 2 seconds. I took it to AutoZone and had the check engine light reset for the O2 sensors turned off and still had 3 Codes reading. 1- Evaporator purge control valve and 2 Ford Manufacturer specific codes. What is and where is the evaporator purge valve and what codes would be Ford specific that would not show on the normal code scanner? Anyway, the car will idle now but still has a slight miss. All plugs have been checked and rechecked, gapped and regapped, and all coils have been checked for proper voltage and resistance. Someone help a guy out and let me know something.