Engine Control Unit, or ECU. Actually with the introduction of OBD-II the name was officially changed to ECM (Engine Control Module). But everyone still knows it as the ECU so let's just keep calling it that so we all understand what we're talking about.

The ECU's of today are very sophisticated computer chips that monitor all the data recorded by the various sensors in the engine. Not only do they monitor the engine, they can also make changes based on the data that was recorded to keep the engine running at it's maximum possible efficiency. When a modification is done on one of our cars, the program that the ECU was running ends up conflicting with what is now going on in the engine. This can cause problems especially at idle when the engine hangs in the dangerously low RPMs or just stalls out. So instead of waiting for the ECU to adjust itself, you might need to reset it manually.

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NOTE: I am not saying this is the only way to reset the ECU. I understand there are many other ways but I have found this way to be easiest and, most importantly, the safest. This was done on a 3rd generation Integra, for 1st and 2nd generations, consult your manual for proper fuse locations. If you still have your stock radio, you will need the security code given to you by your Acura dealer or (hopefully) by the person who sold you the car.

Make sure the car has already been warmed up to normal operating temperature and is turned off. Pop the hood and find the fuse box. It will be on the passenger side next to the battery as you can see in the first picture. Remove the lid and pull out both fuses as pictured in the second picture.

Leave the fuses out for a few minutes to allow all the old data to be wiped out. Plug the fuses back in. It doesn't matter if you plug them in upside down or whatever they don't have any polarity so just make sure you plug the right fuse in the right place and you're all good. Make sure to replace the fuse box cover as well.

Start up the car and let it idle for about 10 minutes. Don't hit the gas pedal during this time. This time allows your ECU to make new data based on how much air it sees coming into. Use this time to reset your radio stations and clock. After 10 minutes is up, turn the car off.

That's it, you're done. Once you start the car up again, the ECU should be aware of the changes to the motor. Have fun!