I have 2003 Express with 156000km on it, it had a misfire ( P0300) when I bought the van. I replaced spark plugs, checked out coils, replaced all 8 injectors and it was still running rough, my code reader did not tell me which cylinder was acting up, so I put everything back together and I needed to use the van to get some materials even while running rough.
while on the highway the truck all off a sudden took off and it had lots of power.
it was weird, now she runs perfect and hopefully it stays the way.
What would cause it to fix it self?