Hi.
I have a Honda Civic 96 DX / coupe, with 145550 miles.
Recently the check engine light was ON. I reset the light, but after 1200 miles it turns on again.
When I stop in a traffic light the RMP goes down under 1000, around 100 RMP.

I review the motor and found that the exhaust manifold was cracked where the upper O2 sensor is located. The manifold and the upper O2 sensor where replaced but the yellow Check Engine motor is still there. I try to reset it, but ones you turn on the motor, after 5-10 seconds running the yellow light come ups.

I jump the service check connector and receive 5 blinks. I reset the ECU again and disconnect the MAP sensor. Jump the service check again and receive codes 3 and 5. After connect the MAP sensor again just 5 blinks are shows.

I have checked vacuum hoses, pipes and connections. Make sure all connectors are secure. The voltage on the conector is fine = 5 volts.

Would you replace the MAP sensor with out continue to do a lot of test?

 

I have found the following information regarding the MAP sensor

The MAP Sensor converts manifold absolute pressure into electrical signals and inputs the ECU. If your CEL or Check Engine Light is ON and the blink code indicates 3 or 5, there is most likely a problem with the MAP Sensor.
Code 3 indicates an electrical problem and Code 5 indicates a vacuum problem in the Manifold Absolute Pressure MAP Sensor System.

5V is applied to the MAP sensor. When ignition switch is on - 3V is relayed to ECU. When engine is at idle - 1V is relayed to ECU.

The output voltage of the sensor decreases with increasing absolute manifold pressure. This enables it to relay to the ECU to adjust the amount of fuel to be expended. For example, before VTEC is engaged, the manifold absolute pressure surges with the increase in throttle and the corresponding electrical signal is relayed via the MAP sensor to the ECU to provide the most favorable air-fuel ratio for the best power output. The manifold absolute pressure or engine load reading is one of four pre-requisites for valve timing change condition or VTEC engagement.

Given the explanation above if the MAP Sensor has failed or is failing, it can cause a host of problems. Symptoms such as:
• Difficulty of starting engine when cold.
• Rough idle.
• Misfire or rough running.
• Failing emission test.
• Loss of power.

• Advice for CEL LED error code 5. Before making conclusions, check vacuum hoses, pipes and connections. Make sure all connectors are secure. Reset ECU and check again. If CEL code 5 appears, it means the MAP Sensor is not capable of holding vacuum anymore and must be replaced.

Run the following test
(1) After resetting the ecu, start the engine and keep rpm at 2000 for one minute and check for CEL.
(2) You can remove the map sensor and start the engine, let it idle and place finger on MAP port on throttle body, there should be vacuum.
(3) Lastly you can apply vacuum to the MAP sensor to see whether it holds vacuum. If there is no proper equip. you can do this via a transparent long hose, fill the hose with water, hose in u-shape with one end connected to MAP sensor, lift the sensor as high as you can and hold it there, the water level should be different and will not return to the same level.

 

Your answer is right in the info you found.