Have you inspected all the coil wire harnesses, cleaned the connectors with CRC Electronic Cleaner, double checked the plugs the O'Reilly kids sold you?

The only code is P0300?

 

well photo they posted after the fact is indeed coil on plug. i guess they own a H3. would be nice if that was stated on OP

 

This is what the new coils are. Sorry if I didn't say it was a 06 H3

 

yes P0300 is the only code

 

Are the new spark plugs gapped correctly. I just had 1 cylinder misfiring after replacing them. I dropped one plug and didn’t think to check the gap.

 

That would cause a cylinder specific misfire! Depending on number of engine cylinders, P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 etc....

 

I don't believe I ever saw a response from the OP whether they checked each spark plug gap and connection as well as reseating each coil. No reason to freak out or look for potential problems elsewhere until you've done that. I'd also get a skinny attachment piece for your vacuum and carefully vacuum out each plug/coil well to ensure nothing foreign is down there causing connection issues. Also gives you the chance to inspect the wells for any oil. Happened to me a few years back and I ended up having to replace my head gasket. Also, did you confirm that everything was hooked up properly when you reattached the air box and hose? Doesn't seem likely that a small issue with a misaligned hose or something would cause a severe rough idle to the point where it dies on you, but important to have everything clamped up right nonetheless. Probably wouldn't throw a P0300 either but just running through options. I dealt with a P0300 and P0420 (still have this one) for ~7 years and it didn't go away until I had good plugs and coils all the way around AND had a new head gasket. Not saying that's your issue, but if you have oil in the wells or on the spark plug threads then it is contributing to the problem at least.

Might as well also point out the obvious and recommend a thorough cleaning of the throttle body and MAF while you've already got it taken apart. My "pavement princess" doesn't see much dirt and those that wheel might not even think twice about it, but your entire engine bay looks pretty dirty. I'd try my best to clean that up if you have time and definitely follow Doc's recommendation of CRC Electronics cleaner on each plug. Extremely doubtful any of the things in this paragraph would cause a P0300, but these have become engrained in my head after years of following this forum so figured I'd mention them.

 

KU, did you have the valve cover gasket or head gasket replaced?

 

May be you had them separated for photo of coils but the picture you posted clearly shows the air cleaner not attached to the throttle body. That would set codes if you tried to run it like that since the MAF is located in the air cleaner side.