My '98 Cavalier Has No Power & Runs Better With the MAP Sensor Unplugged

The manifold absolute pressure sensor on the 1998 Chevy Cavalier measures the changes to vacuum pressure inside the air intake system. The pressure in the intake manifold constantly is changing as the engine speed and engine load change. The vehicle computer reads the voltage signal from the MAP sensor and adjusts fuel delivery accordingly. A faulty MAP sensor often is associated with a check engine light, and trouble codes p0106, p0107 or p0108. When the MAP sensor electrical connector is disconnected, or there is no return voltage to the computer, the computer enters limp mode and adjusts fuel based on engine speed and throttle position. The MAP sensor is located on the right side of the throttle body, and has a vacuum line connected to the bottom of it.

Instructions

Inspection

1

Lift the vehicle hood and support it with the hood prop rod. Allow the engine to completely cool.

2

Remove the two bolts securing the plastic intake outlet resonator to the valve cover. Loosen the clamp at the throttle body inlet and the air intake tube with the screwdriver. Remove the positive crankcase ventilation hose from the resonator. Remove the resonator from the engine.

3

Trace each vacuum line running from the intake manifold, on the front of the engine, to the various components inside the engine bay. Inspect each individual vacuum line for cracks or damage with the flashlight, and replace as necessary.

4

Inspect the intake manifold for any cracks or flaws.

5

Start the engine and allow it to run until idling normal. Clamp the negative lead of the voltmeter to the negative battery terminal.

6

Probe the gray wire on the electrical connector of the map sensor and check the voltage with the voltmeter. The reference voltage from the vehicle computer should read 5 volts. If the voltage is more or less than five volts, there is an electrical short between the computer and the map sensor, and the map sensor is not at fault. Remove the probe from the gray wire.

7

Probe the light-green wire at the map sensor electrical connector. Inspect the voltage signal from the map sensor on the voltmeter. At idle, the output voltage should be no less than 1 volt, and no more than 1.5 volts. If the voltage at idle is outside of the normal operating voltage at idle, the map sensor is faulty.

Removal

8

Disconnect the electrical connector for the MAP sensor.

9

Remove the bolt securing the MAP sensor to the throttle body with the socket and ratchet.

10

Disconnect the vacuum line that runs from the intake manifold to the MAP sensor.

11

Remove the MAP sensor from the engine.

Installation

12

Set the new map sensor into position.

13

Install the map sensor mounting bolt and tighten to 5.7 inch-pounds with the small torque wrench.

14

Install the vacuum line from the intake manifold to the bottom of the MAP sensor. Plug in the MAP sensor electrical connector.

15

Set the air outlet resonator onto the throttle body. Install the air intake tube onto the resonator. Tighten the clamps for the intake tube, and the resonator at the throttle body with the screwdriver.

16

Install the resonator mounting bolts and tighten to 89 inch-pounds with the small torque wrench.