Idle getting suddenly low then raises back on Honda Civic del sol

1) Check the voltage on your Throttle Position sensor. Sometimes when doing swaps, you have to use your old throttle position sensor because the one that came with the swap is almost always broken. The Honda ECU looks for .5 volts when the throttle blade is closed and 4.5 volts at wide open throttle. You can measure this with the aid of Hondata or an Apexi Vafc, or a handy old voltmeter.

2) Unplug your Idle Air Control Valve (IAC), which is located on the back of the intake manifold. Doing this SHOULD cause the idle speed to increase if it functioning properly. If it does not increase, then you have found your problem... go get a new one. If the idle speed does increase, begin to turn the bypass screw on the throttle body and bring the idle of the car down to like 500-600 rpm, then plug back in your IAC valve. This should bring the speed back to a normal 800 or so rpm. In the event that doesn't work...

3) Check your ignition timing and make sure it is at the stock spec. Usually 16*.

4) Chances are now that you have a vacuum leak somewhere. Trace all of the vacuum lines and make sure there is no leak anywhere. Some people use a little bit of lubricant and spray it on the hoses to watch for bubbles. Personally I have never done this; so try at your own risk. If it still doesn't idle properly, keep reading.

5) Did your Throttle Body get bored out at all? Is Air bypassing the blade?

6) Another thing that sometimes causes cars to idle poorly is too much fuel. Do you have a Fuel Pressure regulator? Make sure that it has a vacuum reference and that it is within specs at static idle. Honda recommends 30-38 psi. So anywhere within there would be worth a try. To adjust your pressure at static idle, Hondata suggests that you do it without the car running. Turn the key to "ON" and the fuel pump will prime the system, then you can adjust your fuel pressure accordingly.

7) At this point I began to think it is ECU/ECM( the cars computer) causing the car to run poorly.

To ensure your ECM is O.K., perform the K-Test:

The K-Test: Remove the MAP Sensor connector and turn the ignition switch to ON (not start). Using a multi-meter, check for 5 volts going between the MAP Sensor connector's reference wire (+) and ground. As you look at the connector, this is the socket on the right. Really press the black test lead into a cleaned main ECM ground on the thermostat housing. If the voltage is low, it’s probably indicating ECM failure. Most failed ECMs will record a fraction of a volt. To me, the K-Test is simple, elegant, and accurate.