Its dfi mate, not efi. And the coil packs sit on the dfi module. They are pretty reliable. More likely to be a crank angle sensor, as it runs into the dfi module. Get yourself a decent manual, it will give step by step instructions on checking your coil packs. Basically a resistance reading, so you need a multimeter too. DFI module you wont be able to check. But if there was a loose connection on the side of it that could give you the problems. DFI module, coil pack and crank angle sensor will usually throw error codes at you though, so I dont think it would be the problem anyway. Far more likely that the problem is with the instrument cluster installation. If its possible put your other one back in and see if the problem goes away. Dont go blaming engine parts and start looking at all the expensive fixes, its far more likely to be a self-inflicted problem, especially if you have been changing parts. Make sure you read everything. You sound like youre a person who hears half a story and worries themself when it doesnt make sense (ie checking error codes).