Hi everyone..i have a 2007 Endeavor SE with about 73000 miles on it..I switched over to synthetic 5w20 at about 43000 miles and the car has been running smooth until lately..The check Engine light came on and it said check cylinder 6..I pulled the boot off the plug and took the plug out and the tip had quite a bit of oil on it..I replaced the plug and then the check engine light went off...when I start the truck after sitting for a while the idle is fine..but if i go somewhere then shut the car off for 5 10 min and start it back up again the idle is very rough going from about 750rpm to 250..im also noticing oil consumption where I have to add about a half quart of oil every 1000-1500 miles..I read somewhere that these engines eat oil..Someone had told me that possibly by using synthetics that the valve seals could be bad and thats why the idle is rough..anyone ever have the issue or know if that could be the issue..I believe that the seals are covered under the powertrain warranty which is 10yr/100000 miles..any help anyone could give me would be great thanks....

I also changed out the coil pack just to rule that out and the idle still runs rough