Air Flow meter (AFM) related performance issue- what I found

[Fiatspiderofpowell]

I am posting this as another variant contribution on resolving the issues of a loss of performance at @ 2,000rpm, fluctuating revs, and constant light puffy backfires on the idle, acceleration and deceleration, since it seems that everyone who experiences any or all of these symptoms has a different fix that worked for them...and this worked for me and may work for someone else, but equally it may only apply to my car. Oh well.

Before I got to this stage I had;

- eliminated all air flow leaks;
- replaced voltage regulator;
- replaced vacuum advance unit;
- replaced distributor, rotor, plugs;
- cleaned all grounds;
- cleaned relay connectors;
- cleaned all sensor connectors;
- replaced non-functioning fuel pump;
- tested integrity of wires to/from ECU and relays;
- replaced fuel pressure regulator;
- and a lot of other connector type activities.


The wires I mention below are those that go from the connector block on the AFM to the ECU.

1. White Wire 9's connection.
The connector serving white wire 9, that bends downwards to touch the circuit board (PCB) inside the AFM, tested as an open circuit so it was not actually making contact with the PCB and no signal could travel to the ECU. By pressing down on the connector (with the eraser end of a pencil) so it touched the PCB, my son was able to start the car first time and it ran fairly well. Taking the pencil away brought back rough idle and poor performance.

2. White Wire 27 and 6.
These wires serve the ambient air temperature sensor in the AFM. This sensor sits in front of the air flap.
With the pencil providing the fix for a great start and initial good running (see 1 above), I measured the resistance across these two wires. For about 5 minutes all went well and their circuit showed good readings. Then very light backfire puffing at idle, acceleration and deceleration starting to occur. This issue coincided with a reading across the wires showing an open circuit, so again no readings would get to the ECU, causing an incorrect fuel mixture to be used.

By sheer fluke the open circuit issue resolved itself and a signal again flowed to the ECU, and all backfiring puffs across all ranges stopped and the car ran great. Now, it seems that the ambient temperature sensor of the AFM is not replaceable or repairable so I will be getting another one which will also save me from having to risk soldering wire 9's connector to the PCB.

3. Other Quirky Performance.

A quick and very short term/short distance fix for all poor performance issues and the bouncing rev syndrome that I have experienced is to turn the engine off, wait a minute, then turn it on again. This always brought performance back for a bit. In hindsight, I believe this fix was only "resetting" the AFM ambient temp sensor so it would enable the signal to the ECU until conditions occurred again to stop the signal - the open circuit. Equally, it could be that being at rest, for even such a short time may have been enough for wire 9's connecion to the PCB to re-establish. I am probably wrong, but this car doesn't always seem to operate on 100% logic.

[Snoopy]

Sounds interesting... sometime same problems... but i changed the AFM (another old not new one)... same problem:
Light backfire puffing at idle, acceleration and deceleration starting to occur.