I strongly think you have a simpler problem than you thought being that you say it starts slow and the cranking speeds up before engine fires. This tells me you have a starting system issue. Starting system is composed of the starter, engine ground, starter power wire (B+), and starter relay. Relay is in the fuse box in the engine compartment. I'd ensure the ground is good to the engine first. take some jumper cables and put black on bat negative (-) and the other black jumper on the engine itself, like a clean bolt somewhere of the tow loop they put on.. make sure the clamp bites through the paint if it has any to reach metal. Make sure the cables won't get caught in the fan or belts and try starting it up. If the cranking has become normal like, then it's a sure thing that your engine ground is poor (like me lol). If nothing changes though, then It could likely be a corroded starter power wire or bad starter, but I doubt the starter's bad. A starter with a bad connection be it pos or neg will start off slow and pick up momentum like you describe. I kinda and hoping and suspecting the ground though cause of your high idle issue.. sensors don't function well with improper grounds. goodluck
I don't know about your idle other than the notorious oxidation issue on the tps/maf/iac connectors. clean them, wiggle them, whatever. and see if the idle gets under control. Mine will stay at 1200 till I come to a stop, then it will finally drop to like 900. if i roll again, the idle goes back up.
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