Heres my problem after driving for a short while and slowing down for a red light, or stop sign the car will stumble hard and almost stall out, although it never has. Does not do it every time but at times will do it twice in a row. I have noticed that my air pump will engage after I hear the switch over valve click and then the hard stumble and a good puff of black exhaust. I find it strange the air injection comes on while the car is fully up to temp. Is it possible that a faulty coolant temp sender is sending a bad command to the air injection and the O2 sensor reads a lean condition then commands the injection to over richen causing the stumble? What do you think? Thanks.

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1989 560sec with a few mods.