If they're black you're running really rich, that black is soot. So too much fuel. You might have a coolant temp sensor problem.
A flywheel that light will often affect idle, the RPM drops to idle so fast that the IACV can't catch it and keep it there without overshooting and stalling. It's a common problem.
If you're running that rich then there is even more of an issue trying to keep idle because enough air can't get into the engine to offset that much fuel.
You've just been blindly replacing stuff it sounds like, you need to start actually troubleshooting in a methodical way. This shouldn't be too hard to track down, but just replacing everything in sight to see if it fixes it is a big waste of time and money.