Bullitt94

Most likely.

9165pt0

here is the link where someone posts about white powder on a header, and it being related to a bad idle which is what is happening.
check it out
https://mustangforums.com/m_4113313/tm.htm

mjr46

I hope all the tech responses in the 4.6 section aren't like what I just read..if so: "if burnt valves won't cause a miss then what the hell will??? sounds like the 4.6 sec needs some help...anyway examine your plug wires for burn marks if you feel that is a possibility

9165pt0

yeah i checked all wires. they look fine. I found a post on another site about a mustang having white powder substance on his header after driving, but there were no answers. this is really wierd...and it still wont idle without throttle damn

brentloftis

This powder reappears after every drive? What is its texture, course, fine, very fine? Does it have a smell? Just don't smell to hard in case it is cocain
Just by description it sounds like coolant burned off but every time I have seen this it is not a mound of powder but rather a whitish stain.

9165pt0

haha yeah ima have to snort it lol jk. umm its just like a lil thicker than baby power. kinda like a sand almost, no real odor that i could smell. Umm on the valve cover there is white stains, maybe it is coolant, where would it be coming from?

dudeboy

If it's a coolant leak it will show with a cooling system pressure test

If it's a bad plug wire it will show (visibly) when you run the motor after dark. You will see the spark jumping...
OR, just stick your finger between the wire and header [8D]

9165pt0

ok guys, i found the coolant leak. the gasket between the t/b and egr spacer is moist and wet on the bottom. And right below it is where the white stains are on the valve cover and white powder on the header. Not sure what happened i just put the gasket on about 6 months ago and everything is tight. I guess i will have to get a new gasket, has this happened to any1 else?