P0402/P1400- 2001 Mercury -sable- how to fix

Question

What componet should i start with. Thanks for your help

Answer 1

P0402 EGR (exhaust gas recirculation) flow excessive

Some of the cause for this condition are EGR leaking especially at idle. One of the most popular and overlook for having a excessive EGR flow is the EGR solenoid One of the vacuum lines connect to the EGR valve. If you remove the cap you will expose a vacuum valve just using your finger on the valve port  will cause the EGR to open.which will result in a rough idle this is one way to test for a functioning EGR valve and its passage.If the solenoid ever get plugged with moisture or that filter just get plugged it will keep the EGR open which result in P0402