Air Flow Meter (AFM) Operation and Testing – 2.5L NA

Overview

This guide explains how to test the Air Flow Meter (AFM) on your Porsche 944 with an 8-valve engine, covering the older 1983-1985.5 models (12V input) and newer 1986-1988 models (5V input). The AFM measures incoming air to help the DME computer adjust fuel delivery. A faulty AFM can cause hesitation, stumbling during acceleration, or rough idling. Testing ensures your 8-valve engine performs reliably.

Tools Required

• Voltmeter (multimeter with voltage setting)
• Ohmmeter (multimeter with resistance setting)
• 9V battery (for off-car testing)
• 9V battery connector with leads
• Small female spade connectors (smallest size, for 9V leads)
• 10mm (3/8 inch) wrench (for AFM removal)
• Sharp knife or razor blade (for cutting AFM cover sealant)
• Pencil eraser (for cleaning potentiometer strip)
• Emery cloth or 400-grit sandpaper (for cleaning wiper arm)
• Flathead screwdriver (optional, for prying AFM cover)

Parts Required

None (unless replacement is needed: AFM 944 606 111 00)

Required Additional Procedures

Steps in these procedures are required to complete this process:

• Air Flow Sensor Installation
• Air Flow Sensor Removal

Step-by-Step Procedure

Step 1: Test the Intake Air Temperature Sensor (Combined)

1. Turn off the ignition switch to cut power to the system.
2. Locate the AFM in the engine bay (near the air filter box) and unplug its electrical connector.
3. Connect your ohmmeter to terminals 6 and 22 on the AFM plug (the two outer male pins).

4. Check the resistance with the air temperature between 15-30°C (59-86°F). It should read 1.45-3.3 k-ohms.
5. If it reads infinite ohms (open circuit), the engine may run rich. If it reads near zero (short circuit), it may run lean. Replace the AFM if faulty (944 606 111 00).

Step 2: Test AFM Input Voltage (Installed)

6. Push back the protective sleeve on the AFM connector, keeping it plugged in.
7. Connect your voltmeter to terminals 9 (input voltage) and 6 (ground) on the back of the connector.
8. Turn the ignition switch to the ON position (engine off).
9. For 83-85.5 models: Expect around 12V (minimum 8V). For 86-88 models: Expect 5V ± 0.5V.
10. If the voltage is outside these ranges, check the DME wiring before proceeding.

Step 3: Test AFM Output Voltage (Installed)

11. Move the voltmeter positive lead to terminal 7 (output voltage) and keep the negative lead on ground (e.g., battery negative).
12. With the ignition ON, you should see 150-250 mV with the barn door closed.
13. Slowly push the barn door open through the air filter intake using a smooth, non-metal tool (like a plastic rod).
14. Watch the voltmeter: Voltage should rise steadily to just below the input voltage (e.g., ~11V for 83-85.5, ~4.5V for 86-88) with no drops or jumps.
15. If there are erratic changes, the potentiometer strip may have dead spots. Proceed to cleaning or replacement.

Step 4: Prepare for Off-Car Testing (Combined)

16. Remove the AFM from the car. Follow this link to ensure this step – Air Flow Sensor Removal – is followed accurately.
17. Prepare a 9V battery with a connector and leads. Crimp small female spade connectors onto the bare ends.
18. Connect the negative lead (black) to terminal 4 (ground) and the positive lead (red) to terminal 3 (input) on the AFM connector.

Step 5: Test AFM Voltage Output (Removed)

19. Remove the AFM cover by cutting the silicone sealant bead with a sharp knife or razor blade.

20. Connect your voltmeter: negative lead to ground terminal 2 (inside AFM), positive lead to sensor output terminal 4 (inside AFM).
21. With the 9V battery connected, expect around 0.5V (e.g., 0.463V with a 9.41V battery) with the barn door closed.

22. Slowly open the barn door by hand. Voltage should rise smoothly to ~8-9V (e.g., 8.45V with a 9.41V input) when fully open.
23. If voltage drops or fluctuates, the potentiometer strip is faulty. Proceed to cleaning or replace the AFM (944 606 111 00).

Step 6: Clean and Adjust the AFM (Combined)

24. Clean the potentiometer conducting strip inside the AFM using a pencil eraser. Be gentle to avoid damage.
25. Clean the wiper arm contacts with emery cloth or 400-grit sandpaper. Insert a sheet of paper between the wiper arm and strip, then sand the contacts through the paper to protect the strip.

26. Retest the AFM (repeat Step 5). If erratic voltage persists and grooves are visible, adjust the wiper arm.
27. Place paper between the wiper arm and strip. Push down on both sides of the wiper arm’s back end to bend it slightly, moving the contacts to an unworn strip area.

28. Retest again. If issues remain, replace the AFM (944 606 111 00).

Step 7: Reinstall the AFM (Combined)

29. Reinstall the AFM. Follow this link to ensure this step – Air Flow Sensor Installation – is followed accurately.
30. Tighten the mounting bolts to 20 Nm (15 ft-lbs) using a 10mm (3/8 inch) wrench.

Post Procedure Checklist

• Start the engine and let it idle. Listen for rough running or stalling, indicating a connection issue or faulty AFM.
• Check the AFM connector for a secure fit—no loose pins or wiggling.
• Drive 5 miles (8 km) and monitor for hesitation or power loss. Retest if problems persist.

Sources

• Clark’s Garage Shop Manual
• Porsche 944 Workshop Manual (Volume 2 – Electrics)
• Pelican Parts Technical Article: Porsche 944 DME Troubleshooting