Recently been encountering bad gas mileage, like 10-16mpg city with the 99 z24. All stock, no mods and gas mileage seems to be the worst when it's cold outside. There's no check engine light and the engine runs good. I had the car scanned yesterday with an actron scanner that reads live data. Everything checked out good, but it said that the pcm was in closed loop mode while idling at operating temp. What could be the problem that's preventing it from going into closed loop mode ? There's a bit of black soot on the tailpipe indicating that it's been running rich, but not too the point that it's making the bumper sooty or anything. Maybe a faulty o2 sensor that just hasn't set off the CEL ?
closed loop while idling at op temp is normal operation
OPEN loop would be odd.
you need to clarify your post... you say it is in closed loop while idling then ask why it won't go into closed loop.
Post some data
- MAP sensor at idle, at 40mph
- TPS sensor at idle
etc etc
- 2004 Cavalier - 124k, owned since new
Sorry, it was in open loop at idle, but had it checked again today and it now shows closed loop at idle at operating temp. I don't have any other data though. I had it scanned at autozone and was not ble to scan while driving. The ignition was advanced about 12 degrees and would sometimes spike to 14 degrees then back down to 12. I'm not sure what it's supposed to be at though. This was while idling around 650 rpm at opearting temp.
