Idle and starting problems in a 2001 Mercury Sable 3.0L S DOHC

2001sabledohc

This all started when my engine overheated because I had no oil in it (I know, I've already heard it). I then accidentally put too much oil in it, white smoke, oil light and the next day, I had the oil changed. Oil light would still come on when I stopped. So I bought an oil pressure sensor. The person I asked to put it on accidentally pulled off the coolant temp sensor and broke it in the process, so I had a brand new one put on by someone else. The check engine light then came on and it began having problems starting. It continued to throw a code for the coolant temp sensor and it threw a new one, the throttle position sensor. I could only start it with starter fluid. I replaced the throttle position sensor and the MAF sensor bc it was visibly broken. The codes were cleared and it still has these codes. During a cold start, it turns over but doesn't start. It takes 3-7 tries to get it started when it's cold. After that, it starts first try. It idles up to 2000 rpms at first and drops down to 1000 rpms. During driving, it accelerates by itself sometimes and almost always is idling high. For instance, I got the car up to 60 mph yesterday and took my foot off the gas. It did not lose power. It's like cruise control until it starts slowing accelerating by itself. I have had 3 mechanics look at it and they all just bail out. Please, if you have any ideas, help!! Also, the battery and alternator have been tested!