Little help please?
 

I have a 1995 200sx SE-R SR20DE. I just recently replaced the valve cover gasket and spark plug tube seals. Now im noticing a larger problem. Now the car idles way to low and smokes and leaks from the connection between the headers and the downpipe. is it the exhaust flange gasket or what? Also, when i changed the said gaskets above i had to remove the spark plugs in order to let the 4 inch puddle of oil seep back into the engine from where it had pooled up around the spark plugs and plug wire. Could my idle problem be the fact that the oil fouled either my plug or plug wire? Or is it simply the exhaust flange gasket messing with the back pressure? Or a mixture of both? lol Any help would be greatly appreciated :]

Ask dealer to apply TSB # 346-2000-32 That is a classic issue for that model and TSB will fix it. I have repaired about a dozen that way.