What size torx key do you need to remove MAF sensor on 3800SC impala

Allen wrenches usually come in a set, try 3/8.

P0171 and P0174 are lean codes. There is likely a large vacuum leak or the MAF is bad.

Try starting the car and wiggling the connector for the MAF sensor. Also try tapping the MAF sensor. If the idle changes or the car stalls replace the MAF sensor.

The second shop should recognize that these codes don't have anything to do with the ignition module.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

It would probably be helpful to know what the actual codes are. There is a nice website at:
http://www.obd-codes.com/trouble_codes/
...with possible solutions.

MAF = Mass Air Flow sensor
It will be located between the air filter and the throttle body. Maybe remove the engine cover. I recall that you'll need a special torx bit to remove it. You may be able to spray it with MAF cleaner; available at any parts store for $6?.
Remove the large hose clamps from the throttle body, and unclip the air filter cover. Remove the cover and accordion tube. Hopefully, you can see the inner part of the MAF sensor. spray it a little, wait a couple minutes, spray again, wait.... repeat maybe 5 times. You're trying to spray the one or two little wires that look like resistors. When it is clean, it should be nice and shiny. Do NOT touch the "resistors" with anything but the spray. .

I have a 2002 Impala with 3.8L.
I had a similar problem with mine. As I recall, mine would idle OK, but would chug and buck like crazy on acceleration. Note: I had NO check engine light!
I tried a new coil pack. No help.
Then I swapped the MAF sensor and that took care of it.
You can try to clean it first. It's located between the throttle body and the air filter.
They sell spray MAF cleaner at the parts store.
As I recall you will need a special torx socket to remove the sensor.

I had the same problem with my 2002 Impala w/ 3.8L.
No check engine light.
My problem turned out to be the MAF sensor. I replaced mine, but you could try to clean it first. I've done that on a few other cars.
Here's a picture of where the sensor is located. I took the picture when I had the radiator out, so it may be confusing. It's located on the big tube going from the air filter to the engine. I recall that you have to pull the engine cover off first.
Unplug the connector.
There are two screws holding it in. They may be special security screws that require a special torx drive.

After you get it out, you can try to clean the small, small sensor with MAF cleaner from the parts store. Spray, soak, spray, soak... until it gets shiny clean. Do not use a brush. It has a super fine wire that can be broken. In this picture, you're trying to clean that little thing in the central window suspended between the two posts.

3.8L Engine To Remove:
MAF Location

1. Disconnect the battery ground cable.
2. Remove the fuel injector cover.
3. Disconnect the mass air flow (MAF) sensor electrical connector.
4. Remove the MAF sensor mounting screws.
5. Remove the MAF sensor from the throttle body.

To Install:

1. Position the MAF sensor on the throttle body.
2. Install the MAF sensor mounting screws. Tighten the mounting screws to 27 in lb (3 Nm).
3. Connect the mass air flow (MAF) sensor electrical connector.
4. Install the fuel injector cover.
5. Connect the battery ground cable.

YOU NEED A T20.

Series II 3.8 litre. Remove the cover that is on top of the engine by removing the the oil cap and and the neck into the valve cover.The throttle body will be on the left side of the car the maf sensor is a rectangular box is right on top of the throttle body held in place by tamper proof torx screws and a plug.

It may be the MAF sensor. In needs to be cleaned or replaced. Located on the throttle body, under the engine cover. Might need special anti-tamper Torx sockets to remove. 2 bolts. One wire connector.

I had to replace mine on 2002 3800 V6. Bucked and shook on moderate to hard acceleration at about 3500-4000 rpms.

code PO102 is mass air flow sensor circuit low frequency condition.what it is saying.MAF sensor element hot wire contaminated or sensor failed.MAF sensor signal shorted to ground or grounded circuit problem.MAF sensor wiring routed close to ignition wires generator solenoids or electric motors.PCM has failed.