Posted 10 January 2014 - 05:18 PM
You should test the solenoid first.
Make sure the vacuum lines are in good shape. Start at the sensor, check the line to the solenoid, then follow the line to the engine. On some it goes straight to the engine. Others it goes to a T which splits to the intake manifold and to the fuel pressure regulator. Some have a line that goes to the Evap solenoid under the intake on the passenger side.
The line to the solenoid usually has a white filter in it. The filter is to prevent condensation or fuel vapors from getting to the MAP sensor. Make sure you can blow air through the white filter. If no air goes through it, replace it. Couple bucks at a dealer.
Under the dash by the steering column are two green connectors. Plug those in and turn the Key On. (Do not start it) this sets the ECU in test mode and cycles all of the solenoids and relays on the car.
Make sure the solenoid by the sensor clicks. Then blow air through the port that goes to the engine to make sure air moves through the solenoid.
Air should flow then stop in correlation with the clicking on and off of the solenoid. The solenoid is good.
If no air flows, the solenoid is bad or clogged. If air flows all the time the solenoid is stuck partially open by carbon or dirt. Either of these conditions present, replace the solenoid.
The port that goes to the sensor is open to the engine or to the small black filter on top, depending on if the solenoid is open or closed. Cover the port that goes to the engine with your finger, then blow air into the port that goes to the sensor. Air should flow out through the black filter on top, then should stop in correlation with the clicking of the solenoid.
If no air flows, pull/twist the filter off and try again. If air flows now, the filter is clogged. You may be able to clean it out with some compressed air.
If no air flows after removing the filter, the solenoid is bad or clogged. Replace the solenoid.
MAP sensor testing is easy with a digital voltmeter. Just need a small paper clip. Straighten the paper clip and stick the end into the back side of the connector on the MAP sensor between the wire and the small rubber boot. (The connector is still plugged into the sensor)
Set the voltmeter to DC volts, start the engine. Touch the red probe to the paper clip, and the black probe to a good ground. The negative battery post is best if you can reach it. If not, wire brush the top of one of the strut bolts and use that.
One side of the MAP sensor connector will be the 5v feed from the ECU. Anything less than 4.5v on this pin means you have a connection problem between the ECU and sensor.
The opposite side will be the ground for the sensor and should read 0 volts or very close to it. Up to about 0.1V or 100mV is fine. Above that means you have a bad ground connection between the sensor and ECU.
The center pin of the connector is the signal pin. Connect a vacuum hose straight from the engine to the sensor with the engine running. With vacuum attached to the sensor you should have between 1.5 and 2.0V on the center pin. (Or something close to that)
Remove the vacuum hose and you should see voltage jump up to around 4.0V. This means the sensor is good.
If the voltage stays low, you could have a poor connection, bad sensor, or bad ECU.