Doc,Could a sporadic MOT cause a stumbling cold idle? I have checked the pulse of the MOT. It will start pulsating when I first crank the auto cold After a few minutes it shuts down and does not come back on. When the fan comes on I hear a click from inside the auto from the left side of the steering wheel dash area. Right after the click the auto starts stumbling and triggers the CEL. Once the auto is warm and O2 sensor activated I can reset the CEL and drive all day without a CEL. I found this out yesterday when checking for the MOT pulse after warmup. I removed the MOT and cleaned it out with carb cleaner and contact cleaner then let it set upside down filled with WD40 in both sides. I tapped the WD40 out and reconnected the MOT to the wired plug and started the engine. I then plugged the pulling side vaccuum and the MOT started pulsating and ticking as described in another tread. I then plugged in the other side. After several minutes as the engine began to warm the pulsating stopped and started between the fan starting up. Once the engine was warm The pulsating stayed constant. Is it possible this was/is my source of the problem. I have know light yet but will have to wait till tomorrow to start again on a cold engine.