Should have 3 wires. 2 wires in a black plastic conector are for the pre-heater. Should have batt voltage on 1 and ground on the other. 3rd wire should be green with a white plastic insulator on the harness side and a black rubber boot on the sensor side. This is the signal wire to the ECU. Pull back the rubber boot and leave the wires conected. Conect a voltmeter between this conection and ground. Start and warm up the engine. Within a few minutes the volt meter should start to oscillate between 0 and 1 volt. Usually about .3 to .7V. If the reading remains fixed or iss very slow to respond, replace the sensor. To adjust the AMM, there is an alluminum plug over the adj screw. Drill a couple of small holes in the plug and remove it with snap ring pliers or needle nose. Counter clockwise on the screw will lean it. You may have a bad coolant temp sensor. It's located in the head near cyl 4 under the intake. It's a bitch to access. Another cause of rich mixture is high fuel pressure. Pressure regulators are known to fail. This is usually accompanied by stalling/rough running/poor idle/black smoke.