2014 yz450 w/ 14 hours bad ECU ?

I've been having trouble with my bike for over a month now. This bike is 100% stock. It was running perfect for the first 13 hours then it miss fired a couple of times and now it will run normal for about 10 minutes then after a short break the rpm meter shows that the bike is idling at 4300 rpm when I know it's about 1/2 that speed. If I Rev the motor the Rev limiter kicks in way to early. I bought a gytr tuner so I could check for any error codes and it shows error code 13. In my manual it tells me to check inlet air pressure sensor and if that is OK replace ECU. I have no way to check the sensor so I was going to replace it but after getting the air box out of the way I discovered that that sensor is screwed to the throttle body with an Allen screw that has a tit in the middle so I'm assuming yamaha doesn't want me messing with it. Should I replace the ECU? What could have caused it to go bad?

No, you shouldn't replace the ECU when the ECU is telling you that the MAP sensor is bad.  The screw is likely a "security Torx" rather that a pegged Allen, but either way, you should go by the codes and buy a wrench that will work, or take the bike to a shop, tell them it has a code 13, and ask them to test the sensor. 

These bikes are not your 1988 yz250 take it to a good dealer and have piece of mind that its being fixed properly

I understand the best thing to do is take it to a shop that has the proper diagnostic equipment. I would really prefer not to. I took apart and greased all the electrical connectors and inspected all the wires. Everything looks good.

When I start the bike with the tuner connected and it's running good. The tuner shows 2100 rpm at idle and air pressure at 101 kPa the hour meter also shows 2100 rpm. When it starts to run bad I get error code 13. The tuner still shows rpm is 2100 and air pressure is 101 but the rpm on my hour meter shows 4200 rpm.

In my manual for error code 13 it says check air pressure sensor. It should be 101 kPa at sea level to 1000 feet. If sensor if functioning proper replace ECU.

Air pressure sensor is $100 and ECU is $300. The shop will charge me $175 to diagnose problem.

What should I do?

Take it in that way you won't have to buy one then it turns out to be the other

Replaced intake air pressure sensor. Bike runs like new again.

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