The full code list is available in the PDF attached to the first post in this thread.
Anyway - code 4 is for the air/smog pump. If the pump is running at a cold start, check all the vacuum tubing from the engine, to the solenoid on the fender, and back to the air valve at the pump. None of this affects engine function or power, it's primarily affecting emissions after a cold start. The O2 sensor is probably fine, but if it's old a new one is always a good idea.
Does the smog pump turn on and off like an A/C compressor? I noticed a noise which sounds like a noisy ac compressor when engaged. I was just looking at the smog pump bearing thread. Don't think its the pump because its not constant. I will check all the vacuum lines however. Is there a diagram that shows where all the vacuum lines are?


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Cables will be next!
























