You can pull the stored fault codes yourself. See the 700/900 FAQ section for details. It will be the same for your car with the LH2.4 system. This may give an important clue.
I agree with the other poster who says that AMM cannot be tested with a meter. The meter does not verify it's output. See what happens with it disconnected (turn off ignition first) or swap it. An engine will start and idle fine with AMM disconnected but RPM's and power will be very limited. If problem of fouling goes away you have the problem nailed. You might try disconnecting the O2 sensor as well, the engine should run fine without it as the ECU just substitutes a value.

In the Bentleys manual there is a list of inputs and outputs to and from the ECC from the sensors etc. You could check these before condemning the harness. The way I see it there are 4 items controlling mixture Coolant temp sensor (not guage sensor), AMM output, throttle position switch, fuel pressure reg and O2 sensor. The control by the O2 sensor input is capable of fine mixture adjustment only so this would not be your problem but you might try disconnecting.

The throttle position switch has a full throttle contact which enriches the mixture. Once again engine will run with this disconnected.

In fact an engine will run with the folowing disconnected:
O2 sensor
throttle position switch
AMM (very limited performance but will idle)
coolant temp sensor (will run fine when cold but rough once engine warms up)
fuel pressure reg with vacume line pulled off


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David Hunter