1997 Infiniti Q45 Poor Acceleration,Surging Idle And Service Engine Soon Light On.

This 1997 Infiniti Q45 came in with the complaints of poor acceleration,surging idle and the service engine soon light on. I checked codes and found 9 codes stored. I knew that most were probably induced or false codes so I cleared the codes and then ran the engine till the SES light came back on. It did not take very long. The only codes that returned were for and open Intake Air Temperature sensor (IAT) and P0100, open or shorted Mass Air Flow sensor (MAF)

I found the IAT sensor harness disconnected. you can see it in the picture above and you can see it in the picture below after I had reconnected it. That part was simple.

I next focused on the MAF sensor. It is located between the air filter box and the engine air intake tube. It is shown below with the air filter and cover assembly removed and also with the connector removed.

The test for the sensor is pretty simple. Check the voltage on terminal #1 (white wire) with the key on and the engine off; less than 1 volt, Key on/engine running;1.0-1.7 volts, Engine running between idle and 4000 rpm; Varies between 1 and 4 volts. If the voltage readings are within specifications then the white wire will need to be checked between the MAF sensor and the engine control computer. On this vehicle I found the reading at 0 volts so I continued checking the input power and ground circuits to the sensor by disconnecting the harness connector and testing for power on terminal #3 (red/green wire) and ground on terminal #2 (black wire) with the key on and the engine off. I had both so the diagnosis is a faulty MAF sensor.Testing terminal #1 (white wire) should only be done with a voltmeter and I strongly recommend testing all sensor wiring with a voltmeter.

To replace the MAF sensor, the breather assembly will need to be removed. I started by unhooking the spring latches.

Then I removed the hold down bolt and pulled the cover and filter off.

I finished removing the lower hold down bolts and disconnected the air intake hose from the MAF sensor.

Next, I removed the two retaining nuts and removed the sensor. I then reassembled the air filter assembly in reverse.

The picture above shows the sensor elements within the MAF sensor. If the vehicle would have had lean run codes, this would have been a good place to look for the problem. Over time, lint from the air filter will build up on the elements and leave a very light covering over the sensor and this will cause the sensor to give a false reading to the engine control computer. After finding the build up I will take a very small screwdriver and very lightly rub the lint film from the sensor elements.