Throwing P0102 - replaced MAF, next?

[Rubedizzle]

Hey folks,

1997 3.8L Firebird, had the engine rebuilt just under a year ago due to a spun bearing. Engine itself has been running fine, up until recently when I gave it some gas and felt it jolt a bit. Engine light came on immediately afterwards, and car feels like it doesn't have the power it should all the time. I have noticed for years. Scanned it, got a P0102 error (MAF Circuit Low), replaced the MAF sensor, and even the connector going into the sensor. Air Flow Rate readings always stay the same when scanning, regardless of reving the engine, and even stays at 1.84g/s when the MAF is unplugged.

You can find an assortment of Freeze Frame details below from each time the P0102 code was thrown. I kept clearing the code with the scanner, and then turning the car on and attempting different things (MAF unplugged, MAF plugged, replacing connector wire, etc).

One weird thing about the car that I have noticed for all of the years I have driven it (well beyond the engine rebuild), is that when reving occassionally, it revs up in spurts, you can see and feel it when you rev, almost as if it hesitates then revs, hesitates then revs. This happens more often in the warmer weather . Along with this, when first starting it, and having it in park, it will rev up and down for a bit until it settles down at 800rpm or so (Seeking I have heard it called?).

Finally, both before and after the rebuild: after driving for a while, then parking, and then starting it again 10-20 mins later, it starts up but feels very rough initially, until I give it more gas and get moving. It vibrates like hell during this time, but doesn't throw any additional codes. Seems to also happen more often in the warmer weather, behaved much better during the winter.

Any idea where to go next? System is running closed loop throughout, and I am beginning to wonder if PCM is part of the problem (And has been a problem for years?). Car isn't modified at all aside from a standard rebuild - even has the stock intake/filter as year ago I felt it ran worse with a K&N intake.

Diagnostic InformationMap
Confirmed Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Pending Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Freeze Frame
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)
Fuel system status, Fuel system 1: Closed loop (1) 
Fuel system status, Fuel system 2: Closed loop (1) 
Calculated engine load: 0.8 %
Engine Coolant Temperature: 100 °C
Short Term Fuel Trim - Bank 1: 17.2 %
Long Term Fuel Trim - Bank 1: 0.8 %
Short Term Fuel Trim - Bank 2: 17.2 %
Long Term Fuel Trim - Bank 2: 4.7 %
Intake Manifold Absolute Pressure: 47.0 kPa
Engine RPM: 855 RPM
Vehicle Speed Sensor: 5 km/h
Air Flow Rate from Mass Flow Sensor: 1.84 g/s
Absolute Throttle Position: 0.0 %

Diagnostic information provided by OBDAutoDoctor

Diagnostic InformationMap
Confirmed Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Pending Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Freeze Frame
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)
Fuel system status, Fuel system 1: Closed loop (1) 
Fuel system status, Fuel system 2: Closed loop (1) 
Calculated engine load: 0.8 %
Engine Coolant Temperature: 98 °C
Short Term Fuel Trim - Bank 1: 5.5 %
Long Term Fuel Trim - Bank 1: 0.0 %
Short Term Fuel Trim - Bank 2: 1.6 %
Long Term Fuel Trim - Bank 2: 8.6 %
Intake Manifold Absolute Pressure: 32.0 kPa
Engine RPM: 1489 RPM
Vehicle Speed Sensor: 0 km/h
Air Flow Rate from Mass Flow Sensor: 1.84 g/s
Absolute Throttle Position: 3.9 %

Diagnostic information provided by OBDAutoDoctor

Diagnostic Information
Confirmed Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Pending Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Freeze Frame
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)
Fuel system status, Fuel system 1: Closed loop (1) 
Fuel system status, Fuel system 2: Closed loop (1) 
Calculated engine load: 0.8 %
Engine Coolant Temperature: 96 °C
Short Term Fuel Trim - Bank 1: 2.3 %
Long Term Fuel Trim - Bank 1: 3.1 %
Short Term Fuel Trim - Bank 2: 3.9 %
Long Term Fuel Trim - Bank 2: 6.3 %
Intake Manifold Absolute Pressure: 36.0 kPa
Engine RPM: 819 RPM
Vehicle Speed Sensor: 0 km/h
Air Flow Rate from Mass Flow Sensor: 1.84 g/s
Absolute Throttle Position: 0.0 %

Diagnostic information provided by OBDAutoDoctor

Diagnostic InformationMap
Confirmed Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Pending Trouble Codes
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)

Freeze Frame
P0102: Mass or Volume Air Flow "A" Circuit Low (Powertrain, Generic)
Fuel system status, Fuel system 1: Closed loop (1) 
Fuel system status, Fuel system 2: Closed loop (1) 
Calculated engine load: 0.8 %
Engine Coolant Temperature: 91 °C
Short Term Fuel Trim - Bank 1: 14.8 %
Long Term Fuel Trim - Bank 1: 25.0 %
Short Term Fuel Trim - Bank 2: 14.8 %
Long Term Fuel Trim - Bank 2: 31.3 %
Intake Manifold Absolute Pressure: 35.0 kPa
Engine RPM: 864 RPM
Vehicle Speed Sensor: 0 km/h
Air Flow Rate from Mass Flow Sensor: 1.84 g/s
Absolute Throttle Position: 0.0 %

Diagnostic information provided by OBDAutoDoctor

[GaryDoug]

Re: Throwing P0102 - replaced MAF, next?

Use a multimeter to check the voltage at terminal C (pink wire) of the MAF connector while the ignition is on and the sensor is connected. It should be about 12vdc. If not, there is a wiring problem to the fuse box. Then measure the voltage at terminal B (black/white wire). It should be about zero volts. If not there is a wiring problem to ground. The voltage at terminal A (yellow wire) should be about 3-9 volts DC when the engine is idling (or 12vac), but not 0 vdc or 12vdc. If everything measures good, there may be a wiring problem from terminal A to the PCM.

[Rubedizzle]

Re: Throwing P0102 - replaced MAF, next?

Alright, will definitely check that out Gary, Thanks.

Just something else I realized that might be related, there is a wire that goes on it's lonesome from the over the driver side wheel well over to over top the engine. I am not at the car right now, but from what I remember the wire looks a bit warn, I am unsure if it was part of a remote car starter that was installed (and doesn't work) or not. Any idea if this is something stock vehicles have, or was this done aftermarket? Don't remember it before, but then again don't remember looking at it until it looked worn and crappy.

Example Diagram below:

[FirebirdGT]

Re: Throwing P0102 - replaced MAF, next?

That is not a factory wire.

.

[Rubedizzle]

Re: Throwing P0102 - replaced MAF, next?

Use a multimeter to check the voltage at terminal C (pink wire) of the MAF connector while the ignition is on and the sensor is connected. It should be about 12vdc. If not, there is a wiring problem to the fuse box. Then measure the voltage at terminal B (black/white wire). It should be about zero volts. If not there is a wiring problem to ground. The voltage at terminal A (yellow wire) should be about 3-9 volts DC when the engine is idling (or 12vac), but not 0 vdc or 12vdc. If everything measures good, there may be a wiring problem from terminal A to the PCM.

Hey, so I had a chance to check this out today with a multimeter. I think your Terminal Letters are swapped, my Terminal A was pink, Terminal B black/white, Terminal C Yellow. Terminal A (Pink) was 12.4VDC when on/idle, Terminal B (black/white) was 0V DC at idle, Terminal C (Yellow) was 10.0 V DC at idle. I checked the connections and followed the wires as far as I could, and the wires seem to be in good shape close to the PCM and as far as I could follow them.

It has gotten a bit worse now, starting the car, it seems to have a rougher idle (trying to settle down, revs up, dips down low, revs up, etc..), and hesitates a lot more after I have come from a stop (also when moving, but much more noticable from stop).

Any Idea if it could be a problem with the O2 Sensors, or even the PCM itself? I replaced my MAP sensor today while I had a chance as well, no change in performance, but this sensor is definitely working based on the sensor data.

[GaryDoug]

Re: Throwing P0102 - replaced MAF, next?

I would address the fact that the MAF reading stays stuck at 1.84g/s all the time. It should rise from about 4-5g/s at idle to way higher as the engine speeds up, to maybe 100g/s or more at WOT. Were those readings taken before or after (or both) the MAF sensor was replaced? It is possible that the output from the yellow wire isn't making it to the PCM pin, which is at the blue connector C1 pin 54 (between a white wire and a dark blue wire).
BTW, those pin-to-color references I cited come from the GM factory service manual and might be wrong, but I would recheck the work replacing the connector, just in case.
If you can get your hands on a multimeter that measures frequency, that would be good to test the sensor's output (yellow wire). It should increase in frequency as the air flow increases with higher RPM's

[Rubedizzle]

Re: Throwing P0102 - replaced MAF, next?

Hey GaryDoug - Not a problem, my terminal letters were based off of what was written on the MAF sensor I put in, so who knows if that is even right or corresponding to actual GM . Either way, my colours matched up with the readings you had mentioned. I double checked the way I wired up the connector for the MAF, and it is correct.

The readings were taken both before and after MAF replacement (And even with the MAF not connected), and even today, the readings were the same. 1.84g/s - very odd. I will try to measure the frequency, will keep you posted! Thanks for all the help!