I have a 1991 Jeep Cherokee 4.0 L automatic. Sometimes it runs and shifts fine, most of the time it doesn't. I get error codes for Oxygen Sensor Signal Lean and Alternator Field Switching Improperly. When I first start it up, it idles at 1500 RPM and gradually increase to 2300 RPM. I shut it off and it won't restart. The exhaust smells like straight gas fumes. When I finally get it to restart, it idles at 1300 RPM and drops down to 1000 RPM and back again. About every 4th or 5th cycle of this, it drops down to 500 RPM or less and almost dies with black smoke coming out of the tail pipe. On the road, it won't shift by itself unless I get the engine up to 4000 RPM - 4500 RPM. I can get it to shift at a lower RPM by getting it up to 2800 RPM - 3200 RPM and taking my foot off the gas. Sometimes that doesn't even work and I cruise around town at 30 MPH and 3500 RPM with everyone staring at me. The problem will go away for a few days and come right back, sometimes in the middle of driving it, it will downshift and I have to play footsie with the gas pedal again. I have a feeling it is sensor related, but I don't have much money and don't want to waste it changing parts that don't need to be changed. Any help or advise would be greatly appreciated.
edit: I changed the MAP sensor and nothing changed. Could it be the oxygen sensor? The fact that it has started working fine all by itself a few times makes me think that it is not a vacuum leak.
have the same problem?
Wednesday, February 14th, 2007 AT 4:35 PM