| I am experiencing a problem with my 92, NA. About four weeks ago the engine began idling rough - similar to how an engine would idle with fouled plugs. Over the past few weeks the idle continued to worsen until yesterday when it got considerably worse. In fact, it got so bad that the engine now feels as though it is only running on five cylinders. Engine power is, of course, terrible. The Check Engine lamp itself never illuminated, but I did run a Mode II self-diagnosis on the ECU. I was expecting to see either a code 11 (Camshaft Angle Sensor circuit (CAS)) or 21 (Ignition signal circuit) error. Instead it returned code 33 (O2 Sensor). I then entered MODE II - Heated Oxygen Sensor (O2) Monitor and isolated the O2 issue to the left sensor.
* Left O2 sensor; Check Engine light does not illuminate (Off = Lean).
* Right O2 sensor; Check Engine light blinks normally. My thought is that the O2 sensor is not the cause of the problem, but rather a result there of. The only other test I have done at this point is to meter five of the six ignition coils. (I did not remove the cross over tube to meter the left rear coil.) Of the five coils I did meter, four tested as 0.7 or 0.8 ohms, while the fifth (right bank) was initially 1.6 ohms but eventually settled down to .9 ohms. Also, both rear tail pipes are black. So either a fuel injector is dumping excessive fuel and the plug has become fouled, or the plug is not firing at all. Given the faulty O2 sensor on the left side, I am thinking that the issue may be on the left bank. The next item I plan to test is the Power Transistor module. But because the self-diagnostic on the ECU only returned error code 33 I wanted to ask for guidance before going any further. Can anyone offer any suggestions as to what should be done next? Should I proceed with testing the Power Transistor Module or something else? BTW, the vehicle is completely stock with approximately 60,000 original miles.
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