Where in the hell is the Ignition Control Module
 

2008 HHR 2.2 here, steady P0304, swapped coils, new plugs. been reading that the ICM might be the culprit but.......where is it????

check this thread: https://www.chevyhhr.net/forums/prob...t-27383/page2/

Only 2006 has a ICM. Look at the other culprits; head gasket, valves, timing, injector, frayed/melted wires.

Dang Don, ya beat me to it.

A steady P0304 says head gasket/cracked head to me.

Have you done a plug check Mexdealer? If the #4 plug is suspiciously clean, there's coolant getting into that cylinder and "steam cleaning" the sparkplug.

Of course you are using the proper AC Delco Iridium plugs, right? Off brand plugs will create havoc in Ecotec engines.