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Q: Need help fixing high idle on start up. on 2000 Mitsubishi Diamante

Last November I replaced alternator, battery and both battery cables, (cable from dealer). Prior to this some mechanic replaced one front downstream 02 sensor but replaced the wrong one and code stayed present.
When the starter caught fire because it was a cheap part that was put on by old mechanic, it failed. Everything was going fine after the electrical stuff replaced.
Driving along and car quits, battery died from trying to start it. Got to vehicle later in the day and nursed it home on the freeway at higher(2000 plus) RPMS. Pulled same 02 code for sensor on back bank after the cat. Replaced front sensor because starter caught the wires on fire when the starter burned up...this front sensor is the one the mechanic replaced and he installed it cross threaded. SO i seen smoke coming from the hole and took it too exhaust shop who replaced the bung and installed the 02 sensor again with very few threads left but it worked for now. Smoke problem fixed. Had airbox off vehicle. Code for sensor was still stored for back bank after cat, so replaced it but accidently installed the connector back words because the new sensor appeared to be deceptive on how its installed. Found this problem out and reversed the sensor to normal. Code didnt set though. No codes but on start up the idle goes to 3200 rpms. SO i thought maybe i had a bad air meter and unplugged it and the idle went down, so got a used one from parts yard and no change, so i feel that ruled out the meter causing the problem. I know its possible a used part can be bad but this part came from a good facility with a good reputation of stocking and selling tested parts. Old air meter would not let car idle at all.
Installed the air meter and put the air box back in. Did break one of the plastic tabs(worn plastic junk) where the lock down for the air box holds the air filter in place but this is before the air meter, so this should not affect the meters reading.
I cant find a chart that tells me what the parameters for all the sensors that are on this car and what they should read on the scanner screen.
I dont find any blown fuses.
There is a plunger type device on the backside of the throttle body area where its not anywhere near the other end of what would appear to make contact. I dont even know if this is an issue or not.
Like i said before all was driving down the road and it just stalled. I think it was ran out of fuel so i put fuel into get it home to be sure that wasnt it. The gas gauge I think.
The car sat for a couple months while out of Arizona and the battery died. Any chance the computers not relearning itself properly and causing this. I dont find any leaks by listening and looking for vacuum leaks.
There is also a hole in the flex tube of the exhaust but I dont think this is an issue.
Thank you for the help.
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start with basics. check the compression, fuel pressure and spark. problem is in one of those areas and then we can talk more.

I hope you are still here to help? .....finally got time and used utube...I did not do compression test because problem isnt with the engine, so i feel I am okay to say I dont need it checked. The car is running good its just something I have done to cause this high idle. I drove the car down the street to carwash and it runs good, just high igle.
I removed the air sensor under the throttle body and cleaned it wih mass air sensor cleaner...this turned off the oxygen sensor code that was setting. When removed it came to thought that I used brake parts cleaner to clean the throttle body while back and I didnt know this system enough to realize this sensor has the air ports inside the mouth of the throttle body, so cleaned it all again this time and installed the sensor.....not sure if that brake cleaner damaged this sensor because i dont usually do engine performance repairs on Mitsubishi and send them away to a dealer for diagnosis because its cost effective. Now than, the air boxes air filter has both of the clamped pins broken to hold it in place but this is before the air meter so I dont think this is an issue but you could correct me if wrong. The car starts nicely and runs nicely so I dont think fuel is an issue, the wires and plugs were put on recently and there is no engine miss or rough idle...just that dang steady high idle. I took 3 snapshots of the system with my otc nemesys, so im in the house now trying to figure that out on the laptop what sensors are reading wrong. thank you

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