AFM Adjustment



Cost: none


Time: 40min

Picture courtesy of Jr England - Procedure courtesy of Bill R.

Idle problems can be caused by an Air Flowmeter (therafter AFM) out of adjustment.
Don't attempt to adjust your AFM without an exhaust gas analyser.


  • Hex wrench.
  • Exhaust gaz analyser.

1. With the engine off: check the throttle body butterfly gap. It have 0.002" gap with a feeler gauge at the bottom of the butterfly. Stick a 0.002" gauge in the open throttle plate, let the plate close with the gauge down at the bottom and see how much drag you get removing it. Set the gap with the throttle stop if needed.
2. Warm up the car then shut it off.
3. Disconnect the O2 sensor at the connection. (round black connector).
4. Restart the car and before the catalytic converter gets hot (which it won't with the car just idling) insert the gas analyser in the tailpipe.
5. Adjust the AFF screw the the allowable tolerances, from 0.2 to 1.2. Bill's car is setup to 0.9 to 1.0 and it seems to give a better idle. It also helps get ride of a slight hesitation when accelerating.

The AFM can be turned over to locate the screw then you can turn it back a little bit. (If you turn it completely, you won't be able to insert the hex wrench).
The screw controls how much air bypasses the flapper on the afm. By screwing it in, less air bypasses and it forces the flapper to move further sending a different signal to the dme. Turn the screw in to richen the mixture and out to lean it..

If you plan on doing it without a gaz analyser:
Gradually turn the adjusting screw in very small increments and wait about 30 seconds after wach adjustment to see what it does to the idle. Don't adjust it more than one turn in either direction.

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