I own a 2003 Mitsubishi Lancer, and have been the only owner and mostly the only driver. About a year ago I had a weird misfiring problem where if I pushed the accelerator down more than half way it would stop firing on any cylinders and the car would suddenly slow down (which was interesting when overtaking on the freeway). I took it to a mechanic near my work, they had a look and said there was a leak in the rocker gasket, it had filled a couple of spark wells with oil, and the sparks, spark leads, and ignition coils were arcing. They replaced the rocker gasket, all the sparks, the leads, and two (of four) coils.
Fast forward to now, a year later, the problem has come back. I've taken the car to NRMA (a State service provider in NSW, Australia) for a bunch of work (full service, timing belt, and this misfiring issue). I explained the history of the misfiring issue to the mechanics so they could narrow down the problem. They replaced all the sparks and the spark leads, saying that they were arcing out, but that there was no oil in the wells. I took it out, and noticed the problem was still happening under heavy acceleration, so took it straight back. They couldn't work on it there and then because it was 5:30 Friday, they said to bring it back in a couple of days so they could replace the coils, and that it was safe to drive home for now.
I've driven it home, but now (5 days later, after the New Years break) I've gone to drive it back and I can't. It starts fine, idles fine, but as soon as I give it the slightest hint of gas, it cuts out like it did previously under heavy acceleration. I've tried multiple times over several hours, no luck.
What is likely to have happened here to cause the car to not fire at all now? What parts are likely to need replacing, and could the brand new sparks and leads be burnt out along with the coils? Could it just be a burnt out fuse?